Tilonalli's Skinshifter — ruling 1

If the target of the ability of Tilonalli’s Skinshifter becomes an illegal target, Tilonalli’s Skinshifter won’t become a copy of anything. It will remain a 0/1 attacking creature.

Tilonalli's Skinshifter — ruling 2

Tilonalli’s Skinshifter copies the printed values of the target creature, plus any copy effects that have been applied to it. It won’t copy counters on that creature or effects that have changed its power, toughness, types, color, or so on.

Tilonalli's Skinshifter — ruling 3

Notably, Tilonalli’s Skinshifter won’t copy effects that make a noncreature permanent become a creature. If this causes Tilonalli’s Skinshifter to stop being a creature, it’s removed from combat.

Tilonalli's Skinshifter — ruling 4

If Tilonalli’s Skinshifter copies a creature that’s copying something else, it will become whatever the target is copying.

Tilonalli's Skinshifter — ruling 5

If an effect from a resolving spell or ability, such as that of Rallying Roar, begins to apply to Tilonalli’s Skinshifter before it becomes a copy of another creature, that effect will continue to apply.

Tilonalli's Skinshifter — ruling 6

Because attackers have already been declared, any abilities Tilonalli’s Skinshifter copies that trigger when it or other creatures attack won’t trigger.

Tilonalli's Skinshifter — ruling 7

Once the ability of Tilonalli’s Skinshifter resolves, its new characteristics don’t change if the characteristics of the copied creature change or if the copied creature leaves the battlefield.

Tilonalli's Skinshifter — ruling 8

Tilonalli’s Skinshifter remains a copy of the creature through the end step. Damage is removed from it at the same time that it stops being a copy.

Tilonalli's Skinshifter : règles, fonctionnement et interactions (MTG)

Tilonalli's Skinshifter is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Haste Whenever this creature attacks, it becomes a copy of another target nonlegendary attacking creature until end of turn.

How it works : Tilonalli's Skinshifter

Original English text — Wizards of the Coast / Scryfall

#1September 29, 2017· Wizards of the Coast
If the target of the ability of Tilonalli’s Skinshifter becomes an illegal target, Tilonalli’s Skinshifter won’t become a copy of anything. It will remain a 0/1 attacking creature.
No other card is named in this ruling.
#2September 29, 2017· Wizards of the Coast
Tilonalli’s Skinshifter copies the printed values of the target creature, plus any copy effects that have been applied to it. It won’t copy counters on that creature or effects that have changed its power, toughness, types, color, or so on.
No other card is named in this ruling.
#3September 29, 2017· Wizards of the Coast
Notably, Tilonalli’s Skinshifter won’t copy effects that make a noncreature permanent become a creature. If this causes Tilonalli’s Skinshifter to stop being a creature, it’s removed from combat.
No other card is named in this ruling.
#4September 29, 2017· Wizards of the Coast
If Tilonalli’s Skinshifter copies a creature that’s copying something else, it will become whatever the target is copying.
No other card is named in this ruling.
#5September 29, 2017· Wizards of the Coast
If an effect from a resolving spell or ability, such as that of Rallying Roar, begins to apply to Tilonalli’s Skinshifter before it becomes a copy of another creature, that effect will continue to apply.
No other card is named in this ruling.
#6September 29, 2017· Wizards of the Coast
Because attackers have already been declared, any abilities Tilonalli’s Skinshifter copies that trigger when it or other creatures attack won’t trigger.
No other card is named in this ruling.
#7September 29, 2017· Wizards of the Coast
Once the ability of Tilonalli’s Skinshifter resolves, its new characteristics don’t change if the characteristics of the copied creature change or if the copied creature leaves the battlefield.
No other card is named in this ruling.
#8September 29, 2017· Wizards of the Coast
Tilonalli’s Skinshifter remains a copy of the creature through the end step. Damage is removed from it at the same time that it stops being a copy.
No other card is named in this ruling.