Grendel doesn't have any powers. He's pretty much like Batman in the sense that it's his intellect that's his strongest weapon, only Hunter Rose(Grendel) has his own agendas. His background story's way to long to explain, so I'd say you should look him up on Wikipedia. But he did fight Batman in a crossover & won!
He won in the sense that even though Batman un-masked him, he still didn't know who he was. Batman beat the crap out of him & dislocated his shoulder but it was more of a mental victory that Hunter won. Besides, I love both characters & Matt Wagner did the art & writing chores, making it great.