Mahishasura

Mahishasura enters the battlefield as a copy
of any creature on the battlefield. At the
beginning of each upkeep, Mahishasura can
become a copy of a different creature on the
battlefield. If Mahishasura were to die, exile
him and return him to the battlefield.
"He was finally banished to The Bardo,
to forever spin The Jataka-Mala..."
-Valmiki