Eronthal, the Trapped

Deathtouch, lifelink
Whenever a creature you don't control dies, put
an essence counter on Eronthal, the Trapped.
Then if there are three or more essence counters
on Eronthal, exile Eronthal, then return him to
the battlefield transformed under his owner's
control.
Trapped on a world unknown to him, his only wish to
feel his lover's embrace again.