Clever Impersonator

If the chosen permanent is a token, Clever Impersonator copies the original characteristics of that token as defined by the effect that put that token onto the battlefield. Clever Impersonator is not a token.

You can choose not to copy anything. In that case, Clever Impersonator enters the battlefield as a 0/0 creature, and it's put into the graveyard immediately (unless something is raising its toughness above 0).

If Clever Impersonator enters the battlefield at the same time as another permanent, it can't become a copy of that permanent. You may choose only a nonland permanent that's already on the battlefield.