Always be reduced or enlarged, sometimes he may reduce as well and catch you off guard, but if you keep mixing it up he'll have a very hard time trying to predict what you are. This initial confusion is plenty of time to sing blur, which is what you should be doing ASAP, not using beast call.

Also rest, I know it doesn't do much when he's berserking, but at least if he's not he can't simply open with bash.