Tilonalliâ€™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.
Tilonalliâ€™s Skinshifter copies the printed values of the target creature, plus any copy effects that have been applied to it. It wonâ€™t copy counters on that creature or effects that have changed its power, toughness, types, color, or so on.
Once the ability of Tilonalliâ€™s Skinshifter resolves, its new characteristics donâ€™t change if the characteristics of the copied creature change or if the copied creature leaves the battlefield.
Notably, Tilonalliâ€™s Skinshifter wonâ€™t copy effects that make a noncreature permanent become a creature. If this causes Tilonalliâ€™s Skinshifter to stop being a creature, itâ€™s removed from combat.
If Tilonalliâ€™s Skinshifter copies a creature thatâ€™s copying something else, it will become whatever the target is copying.
If the target of the ability of Tilonalliâ€™s Skinshifter becomes an illegal target, Tilonalliâ€™s Skinshifter wonâ€™t become a copy of anything. It will remain a 0/1 attacking creature.
If an effect from a resolving spell or ability, such as that of Rallying Roar, begins to apply to Tilonalliâ€™s Skinshifter before it becomes a copy of another creature, that effect will continue to apply.
Because attackers have already been declared, any abilities Tilonalliâ€™s Skinshifter copies that trigger when it or other creatures attack wonâ€™t trigger.