Mod never looks the same way twice, so it's hard to peg him with a physical description. He verges from "spot-on realistic" to "obviously a costume" depending on his mood. The costume he seems to use most, simply because it's his most recognizable, is that of a lion with a gold crown and a red cape.
As the king of costumes and the personification of same, he has powers that pertain to costumes.
Mod can:
Because he's not tied to a central body, he can be destroyed an infinite amount of times and still stay alive. Like Mel, his essence lies somewhere else.