What Are Copiable Values?

Dualcaster Mage: When Dualcaster Mage enters the battlefield, copy target instant or sorcery spell. You may choose new targets for the copy.
Opt: Scry 1. Draw a card.
Young Pyromancer: Whenever you cast an instant or sorcery spell, create a 1/1 red Elemental creature token.

When you use Dualcaster Mage’s ETB ability to copy Opt, because the copied spell was not cast, it cannot trigger Young Pyromancer’s cast trigger.

Dualcaster Mage: When Dualcaster Mage enters the battlefield, copy target instant or sorcery spell. You may choose new targets for the copy.
Fling: As an additional cost to cast this spell, sacrifice a creature. Fling deals damage equal to the sacrificed creature’s power to any target.
Pull from Tomorrow: Draw X cards, then discard a card.

Both the amount of damage Fling can deal and the X in Pull from Tomorrow are copiable values of the spell. For example, if you cast Pull from Tomorrow with X=4 and copy it once, that is two instances of draw 4, discard 1. Also note that Fling’s sacrificing a creature is its cost, not its effect, and costs are not copied. So when you copy Fling, you simply choose another target to deal the same damage to. Similar interactions include Galvanic Iteration + Big Score.

Dualcaster Mage: When Dualcaster Mage enters the battlefield, copy target instant or sorcery spell. You may choose new targets for the copy.
Get Lost: Destroy target creature, enchantment, or planeswalker. Its controller creates two Map tokens.
Destroy Evil: Choose one —
• Destroy target creature with toughness 4 or greater.
• Destroy target enchantment.

When you copy a spell, you copy all the decisions made for it, which includes modes. Get Lost has no mode choice when cast, so when you copy Get Lost with Dualcaster Mage you can freely choose which creature, enchantment, or planeswalker to target. Destroy Evil is different: its mode is chosen when it is cast, and that mode becomes a copiable value of the spell. So suppose the original Destroy Evil was cast choosing “Destroy target enchantment.” If you copy it, you can only target an enchantment and cannot choose “Destroy target creature with toughness 4 or greater.”

Dualcaster Mage: When Dualcaster Mage enters the battlefield, copy target instant or sorcery spell. You may choose new targets for the copy.
Memory Deluge: Look at the top X cards of your library, where X is the amount of mana spent to cast this spell. Put two of them into your hand and the rest on the bottom of your library in a random order.
Prismatic Ending: Converge — Exile target nonland permanent if its mana value is less than or equal to the number of colors of mana spent to cast this spell.

There is another kind of information that is easily mistaken for a copiable value: the mana spent to cast a spell. Using the Pull from Tomorrow example above, what is actually copied is the X value you declared, not how much you paid in total to cast the spell. A normal X=4 Pull from Tomorrow costs 6, and perhaps because of Thalia, Guardian of Thraben you paid 7 to cast it, but none of that has anything to do with copiable values; it only cares what your X is.

Back to this example: when you copy a Memory Deluge, the game cannot check how much you paid to cast the original. It only knows that the copied Memory Deluge was cast for no cost (you could also say 0 mana), so it resolves by looking at the top 0 cards of your library. Copying Prismatic Ending is the same: the copy can only exile a nonland permanent with mana value 0. The good news is that it is at least not completely useless, since it can perhaps still kill a token or the like.

Since we’ve mentioned Thalia, Guardian of Thraben and Prismatic Ending, let me also cover a related rules ruling:
Prismatic Ending can be cast targeting any nonland permanent; it’s just that on resolution, if that permanent’s mana value is greater than the number of colors spent, it has no effect. The extra cost added to a spell by Thalia, Guardian of Thraben is also part of what you paid to cast that spell. So if you want to use Prismatic Ending on Thalia, Guardian of Thraben, you can declare X=0, then pay 1 more because of Thalia, so you actually still pay 2 mana to cast it. As long as those 2 mana include two colors, you successfully remove Thalia.

Dream Eater: It’s a 6-mana creature.
Quasiduplicate: Create a token that’s a copy of target creature you control.
Ritual of Soot: Destroy all creatures with mana value 3 or less.

Normally a token’s mana value is 0, but if it is a token that is a copy of a permanent, the mana value is copied too, because the mana cost is one of the copiable values. For example, if I now use Quasiduplicate to create a token copy of Dream Eater, that token is still a 6-mana creature and will not be destroyed by Ritual of Soot.

Reflection of Kiki-Jiki: {T}: Create a token that’s a copy of another target nonlegendary creature you control, except it has haste. Sacrifice it at the beginning of the next end step.
Reckoner Bankbuster: It’s a Vehicle.

Suppose Reckoner Bankbuster has already become a creature through crew, and now I use Reflection of Kiki-Jiki’s ability to create a token copy of Reckoner Bankbuster. Will it be a creature?

To answer this fully you need the Layer concept, but rule 707.2’s definition of copiable values is enough to answer it. The answer first:

This token will be a noncreature Vehicle, but it still has haste, so as long as you can make it a creature, it can still attack.

How do we explain this result? The simple answer is that neither crew’s type-changing nor its power/toughness-defining ability acts on copiable values, so even though Reckoner Bankbuster is a creature right now, those creature characteristics can’t be copied. The deeper answer is left for the Layer column.

Oko, Thief of Crowns (+1): Target artifact or creature loses all abilities and becomes a green Elk creature with base power and toughness 3/3.
Gilded Goose: A creature to copy.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

I have a Gilded Goose that has become a 3/3 Elk through Oko’s +1 ability. Now I let Mirror Image enter as a copy of this Gilded Goose that has become an Elk. What does Mirror Image look like?

Oko’s +1 does many things, including changing types, changing colors, removing abilities, and defining power and toughness, but none of these modifies copiable values, so Mirror Image enters as a copy of a normal Gilded Goose.

Oko, Thief of Crowns (+1): Target artifact or creature loses all abilities and becomes a green Elk creature with base power and toughness 3/3.
The One Ring: A noncreature legendary artifact.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

It is again Oko’s +1, but this time the target that becomes an Elk is my The One Ring. Because The One Ring has become a creature, I can have Mirror Image enter as a copy of The One Ring. By the same principle as the previous example, though, since Oko doesn’t change copiable values, Mirror Image ends up landing as a normal The One Ring, not a green 3/3 Elk. Also, Oko doesn’t erase the name or the legendary supertype, so now I control two legendary permanents both named The One Ring, and under the legend rule I must sacrifice one until only one remains.

Sentinel of the Nameless City: A creature to copy.
Deepfathom Echo: At the beginning of combat on your turn, Deepfathom Echo explores. Then you may have it become a copy of another creature you control until end of turn.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

Suppose I first have Deepfathom Echo become a copy of Sentinel of the Nameless City until end of turn using its own ability, and then have Mirror Image enter as a copy of Deepfathom Echo (which is currently a copy of Sentinel of the Nameless City). What does my Mirror Image look like now? Does it change at end of turn?

First of all, Deepfathom Echo’s ability is different from the Oko example above: it is an ability that truly modifies copiable values, and this holds even for a temporary copy. When another effect tries to copy Deepfathom Echo, it uses the updated copiable values, and it looks only at what the Echo looks like at the moment of copying, regardless of what happens to the original later.

When Mirror Image enters, Deepfathom Echo’s copiable values are the same as Sentinel of the Nameless City’s, so Mirror Image effectively becomes a copy of Sentinel of the Nameless City. At end of turn, Deepfathom Echo’s copy effect ends and it returns to its original form, but Mirror Image stays in the form of Sentinel of the Nameless City.

Sentinel of the Nameless City: A creature to copy.
Deepfathom Echo: At the beginning of combat on your turn, Deepfathom Echo explores. Then you may have it become a copy of another creature you control until end of turn.
Titanic Growth: Target creature gets +4/+4 until end of turn.

Deepfathom Echo is currently its original 4/4. I use Titanic Growth on it to make it 8/8, and then use its own ability to become a copy of Sentinel of the Nameless City, which has 3/4 stats (suppose it explored a land, which doesn’t affect its stats). What are Deepfathom Echo’s stats now?

• 707.4 Some effects cause a permanent that’s already a copy of one permanent on the battlefield to become a copy of a different permanent and remain on the battlefield. This doesn’t trigger enters-the-battlefield or leaves-the-battlefield abilities. If a noncopy effect is currently affecting the permanent, that effect isn’t changed.

From this rule we learn that although Deepfathom Echo’s copiable values are modified to Sentinel of the Nameless City’s 3/4 stats, this doesn’t affect the +4/+4 effect from Titanic Growth, so Deepfathom Echo ends up at 7/8.

Jewel Thief: When Jewel Thief enters the battlefield, create a Treasure token.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.
Deepfathom Echo: At the beginning of combat on your turn, Deepfathom Echo explores. Then you may have it become a copy of another creature you control until end of turn.

I have Mirror Image enter as a copy of Jewel Thief, and separately have Deepfathom Echo become a copy of Jewel Thief. Do I get a Treasure token?

• 707.5 An object that enters the battlefield “as a copy” or “becomes a copy” of … is already a copy of that permanent as it enters the battlefield. It doesn’t enter the battlefield and then become a copy of that permanent. If the rules text being copied includes any abilities that replace the event of entering the battlefield (such as “enters the battlefield with …” or “as [this permanent] enters the battlefield” abilities), those abilities will take effect. Also, any enters-the-battlefield triggered abilities the copy has will have a chance to trigger.

From this rule we can see that Mirror Image enters independently as a new Jewel Thief, and at that time it can create a Treasure token. As for Deepfathom Echo, it never checks the entering moment, so naturally it has no chance to make a Treasure.

Cavern of Souls: As Cavern of Souls enters the battlefield, choose a creature type.
Vesuva: You may have Vesuva enter the battlefield as a copy of any land on the battlefield.
Thespian’s Stage: {2}, {T}: Thespian’s Stage becomes a copy of target land, except it has this ability.

So what if we change the question: when Cavern of Souls entered it named Elemental, and I have Vesuva enter as a copy of Cavern of Souls, and have Thespian’s Stage become a copy of Cavern of Souls. What does each become?

• 707.6 When copying a permanent, the copy effect doesn’t copy choices made for that permanent. However, if an object enters the battlefield as a copy of another permanent, the controller of that object may make the “as [this object] enters the battlefield” choices for it.

Put plainly, it’s much the same as the Jewel Thief example, and what creature type the original Cavern of Souls named doesn’t matter at all. Vesuva enters independently as a new Cavern of Souls, and at that time it can freely choose a creature type. As for Thespian’s Stage, it also never checks the entering moment and has no chance to name a creature type, so becoming a copy of Cavern of Souls is really just giving itself a new card name.

Phyrexian Dreadnought: When Phyrexian Dreadnought enters the battlefield, sacrifice it unless you sacrifice any number of creatures with total power 12 or greater.
Likeness Looter: {X}: Choose target creature card with mana value X in your graveyard. Likeness Looter becomes a copy of that card, except it has flying and this ability. Activate only as a sorcery.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

Suppose I have Likeness Looter become a copy of Phyrexian Dreadnought in my graveyard, and then have Mirror Image enter as a copy of Likeness Looter. What happens?

• 707.9 A copy effect may add modifications or exceptions to the copying process.
• 707.9a Some copy effects give the copy an ability as part of the copying process. This ability becomes part of the copiable values for the copy, along with any other abilities that were copied.

When Likeness Looter becomes a copy of another creature, it is not copied wholesale; the copiable values are modified slightly. After becoming a copy of the target creature card, it “adds” flying and this activated ability to its own copiable values. Then, if Mirror Image enters as a copy of Likeness Looter, it becomes a Phyrexian Dreadnought that additionally has flying and the become-a-copy activated ability. Of course… the ability to sacrifice creatures on entering was copied too, so I hope you have a Stifle ready to deal with your own triggered ability.

Spirited Companion: When Spirited Companion enters the battlefield, draw a card.
Glasspool Mimic // Glasspool Shore: You may have Glasspool Mimic enter the battlefield as a copy of any creature you control, except it’s a Shapeshifter Rogue in addition to its other types.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

• 707.9 A copy effect may add modifications or exceptions to the copying process.
• 707.9b Some copy effects modify a characteristic as part of the copying process. The final set of values for that characteristic becomes part of the copiable values of the copy.

Suppose I have Glasspool Mimic enter as a copy of Spirited Companion. Glasspool Mimic’s ability also slightly modifies its own copiable values, ultimately making its types “Dog Shapeshifter Rogue,” and if Mirror Image then enters as a copy of Glasspool Mimic, naturally its types are also “Dog Shapeshifter Rogue.” Don’t forget that they can both trigger Spirited Companion’s enters-the-battlefield draw ability.

Gideon Jura (0):
Until end of turn, Gideon Jura becomes a 6/6 Human Soldier creature that’s still a planeswalker. Prevent all damage that would be dealt to him this turn.
Gideon Blackblade:
As long as it’s your turn, Gideon Blackblade is a 4/4 Human Soldier creature with indestructible that’s still a planeswalker.
Spark Double:
You may have Spark Double enter the battlefield as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it’s a creature, it enters with an additional loyalty counter on it if it’s a planeswalker, and it isn’t legendary if that permanent is legendary.

Let’s do a mid-article recap and apply the rules mentioned so far to answer this one. It is my turn, and I have a Gideon Jura that became a creature through its (0) ability, and a Gideon Blackblade that is automatically a creature through its static ability. Spark Double enters as a copy of each of these two Gideons. What does each Spark Double end up looking like?

First, without a doubt, this Spark Double will not have the legendary supertype, and this becomes part of its copiable values; if someone later copies this Spark Double, the result will likewise not be a legendary permanent.

Next is the question of whether this Spark Double is a creature and what counters it has. Let’s look at Gideon Jura first. From the earlier definition of copiable values, Gideon Jura’s ability to turn himself into a creature does not affect copiable values, and what Spark Double sees is just an ordinary planeswalker. So it enters as a noncreature planeswalker with an additional loyalty counter.

By that logic, Gideon Blackblade should be the same, since its ability doesn’t modify copiable values either, right? The answer is slightly more complicated. Gideon Blackblade’s ability indeed doesn’t modify copiable values, but the static ability that makes it a creature on your turn is itself part of its copiable values. Spark Double copies that ability along with everything else, and it already applies as Spark Double enters. So if you copy Gideon Blackblade with Spark Double, it enters with the types “Creature Planeswalker,” and because it has both types as it enters, it gets an additional +1/+1 counter and an additional loyalty counter.

Ob Nixilis, the Adversary: Casualty X. The copy isn’t legendary and has starting loyalty X. (As you cast this spell, you may sacrifice a creature with power X. When you do, copy this spell. The copy becomes a token.)
Esika’s Chariot: Whenever Esika’s Chariot attacks, create a token that’s a copy of target token you control.

Speaking of creating nonlegendary planeswalker tokens, Ob Nixilis with Esika’s Chariot is also a classic example. Ob Nixilis, the Adversary’s casualty changes the characteristics of the token it ultimately produces. Losing the legendary supertype is easy to understand, and the Ob Nixilis token’s starting loyalty being the X defined at casualty is also easy to understand (suppose the creature sacrificed to casualty was The Ancient One, so X is 8). But if I use Esika’s Chariot to create a token copy of that Ob Nixilis token, is the copy token’s starting loyalty 3 or 8?

How Ob Nixilis, the Adversary really works is a bit deep and a bit convoluted, so here is just the simple conclusion: casualty creates a copy of a permanent spell whose copiable values have been modified, and when that spell resolves it produces a permanent with the corresponding characteristics. So the Ob Nixilis token that was originally made by casualty with The Ancient One has a copiable starting loyalty of 8, and a token copy of it will likewise be a nonlegendary Ob Nixilis, the Adversary with starting loyalty 8.

Spirited Companion: When Spirited Companion enters the battlefield, draw a card.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.
Altered Ego: You may have Altered Ego enter the battlefield as a copy of any creature on the battlefield, except it enters with X additional +1/+1 counters on it.

• 707.9e Some replacement effects that cause a copy effect include an exception that is itself an additional effect (rather than a modification of the affected object’s characteristics). If another copy effect applies to the object after the copy effect with such an exception, that exception’s effect doesn’t happen.

This is an extremely tricky and rare special case. You can just skim it, and it’s no problem to pass over it if you don’t follow. Suppose I have a Spirited Companion and a Mirror Image on the battlefield, and Mirror Image did not enter as a copy of any creature. Now you have Altered Ego enter as a copy of Mirror Image, and because of Mirror Image’s own replacement effect you choose to copy Spirited Companion as it enters. In the end you will not be able to put X additional +1/+1 counters on it through Altered Ego’s original replacement effect.

Moritte of the Frost: You may have Moritte of the Frost enter the battlefield as a copy of a permanent you control, except it’s legendary and snow in addition to its other types and, if it’s a creature, it enters with two additional +1/+1 counters on it and has changeling.
Lair of the Hydra: {X}{G}: Until end of turn, Lair of the Hydra becomes an X/X green Hydra creature. It’s still a land. X can’t be 0.

Suppose I first make Lair of the Hydra a 1/1 Hydra land creature, and then have Moritte of the Frost enter as a copy of Lair of the Hydra. What are Moritte of the Frost’s characteristics at that point?

• 707.9f Some exceptions to the copying process only apply if the copy is or has a certain characteristic. To determine whether such an exception applies, consider what the characteristics of the permanent resulting from the copy effect would be if the exception were not applied, taking into account any other exceptions that effect includes.

Let’s review once more: does Lair of the Hydra’s ability to become a creature modify copiable values? Clearly not, so Lair of the Hydra’s current stats are actually irrelevant. Moritte of the Frost will enter only as a copy of a land, additionally with the legendary and snow types. These two types are written into its copiable values. Because Moritte of the Frost is not entering as a creature, it gets no +1/+1 counters and no changeling.

Graveyard Trespasser // Graveyard Glutton: A transforming double-faced creature card. (Hereafter called the “black werewolf.”)
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

• 707.8 When copying a merged permanent or another double-faced card, use the copiable values of the permanent’s currently face-up characteristics to determine the characteristics of the copy.

If you make a permanent a copy of a transforming double-faced permanent, for example making Mirror Image a copy of the black werewolf, the black werewolf’s copiable values are whichever face is currently up, and this copy effect can’t see the other face’s copiable values at all. Suppose the black werewolf is currently the back-face Graveyard Glutton: Mirror Image becomes a copy of Graveyard Glutton, and even if day and night later change and the black werewolf transforms back to the front-face Graveyard Trespasser, Mirror Image still looks like Graveyard Glutton.

Graveyard Trespasser // Graveyard Glutton: A transforming double-faced creature card. (Hereafter called the “black werewolf.”)
Quasiduplicate: Create a token that’s a copy of target creature you control.

• 707.8a If an effect creates a token that’s a copy of a transforming permanent or a transforming double-faced card not on the battlefield, the created token is a transforming token that has both a front face and a back face. The characteristics of each face are determined from the copiable values of the same face of the permanent it is a copy of, as modified by any other copy effects that applied to that permanent. If the token is a copy of a transforming permanent with its back face up, the token enters the battlefield with its back face up. This rule does not apply to tokens that are created with their own characteristics and enter the battlefield as a copy of a transforming permanent due to a replacement effect.

Creating a token copy of a transforming double-faced permanent or card is a bit more complicated. The token checks the copiable values of both faces of the original and copies them onto its corresponding faces. For example, if I use Quasiduplicate to create a token copy of the black werewolf, that token will also follow the black werewolf’s transform rules and transform to the corresponding face when day and night change.

Note, though, that creating a token copy is a relatively special case; generally, when checking copiable values you can still only see the information of the face that is currently up.

Graveyard Trespasser // Graveyard Glutton: A transforming double-faced creature card. (Hereafter called the “black werewolf.”)
Dollhouse of Horrors: {1}, {T}, Exile a creature card from your graveyard: Create a token that’s a copy of the exiled card, except it’s a 0/0 Construct artifact in addition to its other types and has “This creature gets +1/+1 for each artifact you control.” It gains haste until end of turn. Activate only as a sorcery.

Let’s put together the rules mentioned above. What happens if you create a token copy of a transforming double-faced permanent or card, and then modify that token’s characteristics?

• 707.9 A copy effect may add modifications or exceptions to the copying process.
• 707.9a Some copy effects give the copy an ability as part of the copying process. This ability becomes part of the copiable values for the copy, along with any other abilities that were copied.
• 707.9b Some copy effects modify a characteristic as part of the copying process. The final set of values for that characteristic becomes part of the copiable values of the copy.

Suppose you use Dollhouse of Horrors to create a token copy of the black werewolf. As in the previous example, this token copies the corresponding copiable values on both faces and can transform according to its own day/night rules. However, on either face, the copiable values will be modified by Dollhouse of Horrors: the types gain artifact and Construct, the stats become 0/0, and it has “This creature gets +1/+1 for each artifact you control.” As for the haste until end of turn, it is not a copiable value, so if you copy this token again, the resulting creature will not have haste.

Ludevic, Necrogenius // Olag, Ludevic’s Hubris: Can transform into Olag, Ludevic’s Hubris.
Olag, Ludevic’s Hubris: When this creature transforms into Olag, Ludevic’s Hubris, it becomes a copy of a creature card exiled with it, except its name is Olag, Ludevic’s Hubris, it’s 4/4, it’s a legendary blue and black Zombie in addition to its other colors and types.
Enduring Angel // Angelic Enforcer: If you would lose the game, instead transform Enduring Angel and your life total becomes 3. Then if Enduring Angel didn’t transform this way, you lose the game.

This is a classic example also mentioned in Transforming Double-Faced Cards and Copy Effects, so let’s quickly review it once more.

You transform Ludevic, Necrogenius into Olag, Ludevic’s Hubris, which becomes a copy of Enduring Angel. Later your life drops to 0, so Enduring Angel’s ability applies and your life total becomes 3. What does your Olag look like afterward? Will it cause you to lose the game due to Enduring Angel’s ability?

First, Olag is itself a transforming double-faced card and can perform the transform action, so you won’t be hit by Enduring Angel’s lose-the-game rule. Then what does Olag look like after transforming?

• 712.8a While a double-faced card is outside the game or in a zone other than the battlefield or stack, it has only the characteristics of its front face.
• 712.18 When a transforming double-faced permanent transforms, it doesn’t become a new object. Any effects that applied to that permanent will continue to apply to it after it transforms.

Based on the two rules above, when Olag becomes a copy of Enduring Angel, it looks at Enduring Angel’s copiable values, and at that time Enduring Angel’s copiable values include only its front-face information, so Olag has no idea what Enduring Angel’s back face looks like. Once the copy effect is established, Olag always has an effect modifying its copiable values saying “this card becomes a copy of Enduring Angel.” Transforming doesn’t leave the battlefield and doesn’t make it a new object, so even when Olag transforms, this effect continues to apply.

So the final result is that each time your life drops to 0, this creature transforms between the Ludevic, Necrogenius and Olag, Ludevic’s Hubris faces, but because it still has the copiable-values-modifying effect “this card becomes a copy of Enduring Angel,” in the end you will see that the creature’s characteristics are still those of Enduring Angel. You now have an angel that can lock your life total indefinitely as long as it stays on the battlefield.

Erayo, Soratami Ascendant // Erayo’s Essence: A flip card. Its normal state is a legendary creature (Erayo, Soratami Ascendant), and when flipped it is a legendary enchantment (Erayo’s Essence).
Copy Enchantment: You may have Copy Enchantment enter the battlefield as a copy of any enchantment on the battlefield.

Suppose I currently control Erayo’s Essence (its status is flipped), and have Copy Enchantment enter as a copy of Erayo’s Essence. What does this Copy Enchantment look like?

• 110.5b Unless a spell or ability instructs otherwise, a permanent enters the battlefield untapped, unflipped, face up, and phased in.

Unlike transforming double-faced cards, when you copy a flip card, the information of both the top and bottom halves is copied; the characteristics that show are simply determined by your current status. Erayo’s Essence is an enchantment, so Copy Enchantment may choose to enter as a copy of Erayo’s Essence, but when it actually enters it finds its status is “unflipped,” so it ends up entering as a copy of Erayo, Soratami Ascendant. And because Erayo, Soratami Ascendant and Erayo’s Essence are cards with two different names, this avoids the sacrifice from the legend rule.

Deepfathom Echo: At the beginning of combat on your turn, Deepfathom Echo explores. Then you may have it become a copy of another creature you control until end of turn.
Jushi Apprentice // Tomoya the Revealer: A flip card. Its normal state is a creature (Jushi Apprentice), and when flipped it is a legendary creature (Tomoya the Revealer). Currently flipped.
Erayo, Soratami Ascendant // Erayo’s Essence: A flip card. Its normal state is a legendary creature (Erayo, Soratami Ascendant), and when flipped it is a legendary enchantment (Erayo’s Essence). Currently in its normal state.

Suppose I first have Deepfathom Echo become a copy of Tomoya the Revealer. Because Deepfathom Echo’s status is “unflipped,” it ends up becoming Jushi Apprentice. Now I use the flip ability copied over to flip it into Tomoya the Revealer (because it’s a legendary creature, I have to sacrifice until no same-named permanents remain; here I choose to sacrifice the original). At end of turn the copy effect ends and it turns back into Deepfathom Echo, but it keeps the “flipped” status. Next turn, I have Deepfathom Echo become a copy of Erayo, Soratami Ascendant. Because my status is now “flipped,” the result of the copy is Erayo’s Essence.

Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.
Grim Haruspex: Morph {B}

Grim Haruspex is currently face down, and Mirror Image enters as a copy of it. Mirror Image becomes a colorless 2/2 creature with no name, types, abilities, or mana cost, because these are the copiable values of a face-down permanent (as defined by rule 708.2a).

Akroma, Angel of Fury: Morph {3}{R}{R}{R}.
Blade of Shared Souls: Whenever Blade of Shared Souls becomes attached to a creature, for as long as Blade of Shared Souls remains attached to it, you may have that creature become a copy of another target creature you control.
Grim Haruspex: Morph {B}

Suppose I now control a face-down Akroma, Angel of Fury and a face-up Grim Haruspex, and use Blade of Shared Souls to make Akroma a copy of Grim Haruspex. Although you copy Grim Haruspex’s characteristics, because Akroma’s current status is “face down,” you are still a colorless 2/2 (..and so on). At this point, if you want to pay a morph cost to turn Akroma face up, you pay Grim Haruspex’s {B}, not Akroma’s original {3}{R}{R}{R}, because you copied that characteristic as well, and after turning face up you will be a copy of Grim Haruspex.

Akroma, Angel of Fury: Morph {3}{R}{R}{R}.
Blade of Shared Souls: Whenever Blade of Shared Souls becomes attached to a creature, for as long as Blade of Shared Souls remains attached to it, you may have that creature become a copy of another target creature you control.
Graveyard Trespasser // Graveyard Glutton: A transforming double-faced creature card.

Again with a face-down Akroma, Angel of Fury, what if it now becomes a copy of Graveyard Trespasser (front face) using Blade of Shared Souls?

First, one thing must be made clear: although face-down permanents and double-faced cards both physically flip back and forth in actual games, the two are completely different concepts. You can think of a double-faced card as two cards, each with its own card back, glued together. When they are turned face down they are no different from an ordinary card, and there is no such thing as face down = transformed.

After the copy effect is established, Akroma becomes a face-down Graveyard Trespasser. Since it is face down, its characteristics are still a colorless 2/2 creature, and you have already lost Akroma’s morph cost, and Graveyard Trespasser itself has no morph cost, so this Akroma can no longer turn itself face up by its own power. Suppose you force Akroma face up by some outside means: it will be a copy of Graveyard Trespasser, locked to the front-face characteristics at the moment of copying. Even if day/night has by now switched to night, Akroma stays as the day-side Graveyard Trespasser and does not become a copy of Graveyard Glutton.

Dreamtail Heron:
Mutate {3}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flying.
Whenever this creature mutates, draw a card.
Gifted Aetherborn: Deathtouch, lifelink.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

Suppose you now mutate Dreamtail Heron onto Gifted Aetherborn. You can freely choose whether to put Dreamtail Heron on top or underneath. Choosing Dreamtail Heron on top gives the result on the left of the image below, and putting Dreamtail Heron underneath gives the result on the right.

This is also the copiable values of this permanent now. If you later use Mirror Image to copy this mutated creature, you will get exactly the same result as in the image above.

Double Major: Copy target creature spell you control, except it isn’t legendary if the spell is legendary.
Ivy, Gleeful Spellthief: Whenever a player casts a spell that targets only a single creature other than Ivy, Gleeful Spellthief, you may copy that spell. The copy targets Ivy.
Gemrazer: Mutate {1}{G}{G}.

A mutating spell is a creature spell that targets a creature, so both Double Major and Ivy, Gleeful Spellthief can copy it. Note, though, that Double Major doesn’t let you choose new targets, so the copied mutating spell still targets the same creature, while Ivy, Gleeful Spellthief forces the copy to target her.

Porcuparrot: {T}: This creature deals X damage to any target, where X is the number of times this creature has mutated.
Mirror Image: You may have Mirror Image enter the battlefield as a copy of any creature you control.

Porcuparrot’s ability checks how many times it has mutated (X can also be simply understood as the number of components in the pile minus 1). Suppose a Porcuparrot that has mutated twice is copied by Mirror Image. How much damage can Mirror Image deal by activating Porcuparrot’s ability? The answer is X=0. How many times a permanent has mutated is not part of its copiable values; to Mirror Image, the whole mutated stack of creatures is like a single object that has always looked this way.

Majestic Auricorn: Whenever this creature mutates, you gain 4 life.
Grim Haruspex: Morph {B}
Dreamtail Heron: Whenever this creature mutates, draw a card.

Now for something more exciting: what happens if you mutate onto a face-down creature? Besides the rules about face-down permanents mentioned earlier, the most important rules for mutate here are these two:

• 725.2e If a merged permanent contains both face-up and face-down components, its status is determined by its topmost component. If a face-down permanent becomes face up because of something it merged with, other effects don’t treat it as having been turned face up.
• 725.2f If a merged permanent is turned face down, each face-up component that represents that permanent is turned face down. If a face-down merged permanent is turned face up, each face-down component that represents that permanent is turned face up.

Let’s start with a simpler situation. Suppose I have a face-down Grim Haruspex, currently a colorless 2/2 creature with no subtypes, and I mutate Dreamtail Heron onto Grim Haruspex (no subtypes = not Human, satisfying the mutate restriction):

• Scenario A: Dreamtail Heron on top, face-down Grim Haruspex underneath
  You end up with a Dreamtail Heron, and the “draw a card when it mutates” ability triggers. But with the face-up Dreamtail Heron on top, the whole pile of permanents counts as face up, so Grim Haruspex can no longer turn face up by paying its morph cost.

• Scenario B: Face-down Grim Haruspex on top, Dreamtail Heron underneath
  You still see a colorless 2/2 face-down creature, and Dreamtail Heron’s mutate-draw ability doesn’t even trigger, because your pile of permanents is face down. Grim Haruspex can pay the morph cost to turn face up, and once it is turned face up, Dreamtail Heron’s abilities come back too. But because you have missed the mutate timing, Dreamtail Heron will not let you draw a card at the moment of turning face up.

With the principle above understood, we can extend the question: suppose it is again a case that has already mutated, with face-down Grim Haruspex on top and Dreamtail Heron underneath, and now I mutate Majestic Auricorn onto this pile, choosing Majestic Auricorn on top. What happens?

Now the topmost permanent is face up, which is in effect the same as Scenario A above, and the whole pile of permanents counts as face up. So Majestic Auricorn’s and Dreamtail Heron’s abilities both trigger normally, and because your pile is face up, the Grim Haruspex in the middle cannot pay its morph cost to turn face up; in this pile it is now just a vanilla creature with no abilities.

Serra Angel: Flying, vigilance.
Gifted Aetherborn: Deathtouch, lifelink.
Blade of Shared Souls: Whenever Blade of Shared Souls becomes attached to a creature, for as long as Blade of Shared Souls remains attached to it, you may have that creature become a copy of another target creature you control.
Gemrazer: Reach, trample. Mutate {1}{G}{G}.

Suppose you equip Blade of Shared Souls onto Gifted Aetherborn and make it a copy of Serra Angel, then mutate Gemrazer onto Gifted Aetherborn, choosing Gemrazer on top. What kind of creature do you get? And what changes after Blade of Shared Souls is unattached?

• 613.2a Layer 1a: Copiable effects are applied. This includes copy effects and changes to an object’s base characteristics determined by the object merging with a permanent.
• 725.2a A merged permanent has only the characteristics of its topmost component, unless the effect that merged it says otherwise. This is a copiable effect whose timestamp is the time the objects were merged.

It’s fine if you don’t follow the two rules cited above, since some concepts will only be explained in later installments. The short conclusion is that copying a permanent and the characteristic changes from mutating a creature are abilities at the same level, and when both occur, the newer change overrides the older one.

Back to the example: once Gemrazer’s mutate is complete, the component underneath currently has Serra Angel’s characteristics, so Gemrazer will have flying and vigilance. When Blade of Shared Souls is unattached, Gifted Aetherborn returns to its original characteristics, so Gemrazer will have deathtouch and lifelink.

Taken alone, this question seems intuitive and not very tricky, but combined with the life-locking angel example (Olag, Ludevic’s Hubris + Enduring Angel) from the double-faced section above, it is very easy to get confused. This can only be put down to mutate’s rules being very special. Whenever you run into a mutate-related case, I recommend always treating it as a special case, so that at least you don’t wreck your understanding of ordinary copy effects along with it.