Azathoth

Flying, Haste, Deathtouch, Menace, Triplestrike, Hexproof.
{5}{b}{b}{b}{b}{b}Monstrosity 10 (if this creature isn't monstrous, put ten +1/+1 counters on it and it becomes monstrous)
When this creature becomes monstrous, destroy half off your opponents creatures rounded down.