Eren, Suicidal Maniac

Flying, first strike
At the beginning of each end step, if three or
more nontoken creatures have died under your
control this turn, you may pay {2}{w}{w}{g}{g}. If
you do, exile Eren from the battlefield or from
your graveyard, then return it to the battlefield
transformed under your control.
"I'll kill every last titan and break free from
these walls!"