#TheBiHanMovieMovewise he has a small kick, a hammer punch, sometimes he'll make like the Three Dirty Dwarves and pound the earth causing debris to bang you on the head. Or he can just throw your ass down.
Now, he can't be frozen, and Sub's attacks don't do much in the way of damage, so how do you effectively beat this boss?
Well, there's a switch on the otherwise of his arena. It lowers an elevator, no idea why its there in universe, but...
The best way to get to it is to try sliding under Grimm. I mean if he doesn't kick you out of it.
Lure Ben "koranot" Grimm to the drop point and the elevator will drop right on his head for a nice chunk of damage. Downside is it takes a while for the elevator to head back up and become usable.
But basically you beat him by invoking the old Animaniacs "anvil on head" gag. SO...
That platform's brown and grubby!
It's very heavy too!
So watch out my rocky friend,
or it will fall on you!