Ego

Trample, shroud
Whenever Ego deals combat damage to a player, as you cast spells from your hand this turn, they gain cascade. (When you cast the spell, exile cards from the top of your library until you exile
a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom of your library in a random order.)
When Ego dies, return it to the battlefield transformed under its owners control.