Tilonalli's Skinshifter

• WWizards of the Coast2017-09-29
  Official Ruling
  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.
• WWizards of the Coast2017-09-29
  Official Ruling
  If Tilonalli’s Skinshifter copies a creature that’s copying something else, it will become whatever the target is copying.
• WWizards of the Coast2017-09-29
  Official Ruling
  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.
• WWizards of the Coast2017-09-29
  Official Ruling
  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.
• WWizards of the Coast2017-09-29
  Official Ruling
  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.
• WWizards of the Coast2017-09-29
  Official Ruling
  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.
• WWizards of the Coast2017-09-29
  Official Ruling
  Because attackers have already been declared, any abilities Tilonalli’s Skinshifter copies that trigger when it or other creatures attack won’t trigger.
• WWizards of the Coast2017-09-29
  Official Ruling
  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.

Rulings via Scryfall