Ditto

When Ditto enters the battlefield target player
exiles cards from the top of their library until
they exile a creature card. Ditto becomes a copy
of that card except it has {c}{c},{t}: Exile Ditto
then return it to the battlefield at the beginning
of your next endstep. Put the remaining cards on
the bottom of its owners library.
Ditto has the ability to reconstruct its entire cellular structure into whatever it sees.