With all cards in play, cast another creature.
Cathars' Crusade's ability will trigger, put a +1/+1 counter on Scurry Oak
Scurry Oak's ability will trigger, creating a 1/1 token
Oggre Battledriver's ability will give +2/+0 and haste to the token.
Cathars' Crusade's ability will trigger again.
Repeat the process for infinite tokens and infinite damage.