If Creature A enters the battlefield as a copy of a creature with a temporary clone effect like that of Shapesharer, does Creature A mantain the temporary nature of that copy effect or does it permanently remain as whatever the other creature currently is?
Creature A will permanently be whatever the Shapesharer temporarily copied. When you apply creatue A's copy effect, you copy all copiable values of the other creature at that time (as modified by the temporary copy effect) and those values become creature A's copiable values for as long as creature A's copy effect is active. Without any duration specified it lasts indefinitely.
Creature A will enter as a copy of that creature and acquire its "copiable values" (C.R. 706.2), and how long creature A will keep those values is independent of how long the effect on the other creature lasts. For instance, if creature A is Clone, the effect lasts as long as it's on the battlefield. If creature A is Vesuvan Shapeshifter, it lasts until Vesuvan Shapeshifter is turned face down.
Former Rules Advisor
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