Trample, Haste

Whenever Bearstine, Consumed by Hate attacks, he gets +X7+0 where X is the number of creatures in your graveyard. He then gains +X/+X where X is the number of Legendary cards in your graveyard.

Next Step - At the end of your turn, if creatures you control have a combined power of 15 or more, remove Bearstine, Consumed by Hate from the game. Bearstine, Fire of Desire is your new commander.