Eren, Vengeful Cadet

ODM (This creature gains flying when attacking)
If an opponent controls a creature with power 5 or greater, Eren, Vengeful Cadet gets +1/-1 and attacks that opponent each turn if able.
During your upkeep, if Eren, Vengeful Cadet is in your graveyard, return it to the battlefield and transform it.
"I promised I'd kill them all. Every last one!"