Bratha, By Some Accounts

Hexproof, menace
At the beginning of your upkeep, if Bratha is in exile, you may flip a coin for each creature on the battlefield. For each win, you may put a -1/-1 counter on that creature.
Whenever Bratha, By Some Accounts enters the battlefield, add X mana of any combination of colors. X is the number of -1/-1 counters on creatures you control.