I'm imagining a more or less normal guy but he probably has a green suit or robe under the jacket and is likely the most muscular of his fellow Admirals. Another real question is, what devil fruit? Im thinking it's a mythical Zoan.
It's got to be a paramencia of high order like Kuma's or Law's. I think it's based on gravity or earth aspects. It could be either. He made the hole and brought down a meteor. Either instance could be based on earth/stone manipulation or gravity manipulation, although I'm leaning towards gravity. I really want to see more of what he can do. Based on last week's panel it seems he and Doflamingo are doing ok, bu Law was injured. It once again shows that the Admirals stand a bit above the warlords with the possible exception of the top 3 (Don, Kuma and Mihawk).