Putting this thing in the Fairy egg group is a massive stretch. If the Volbeat family didn't get the Fairy egg group, there's no way this should.I'm going to assume Bug/Fairy groups for this.
Bug is the only one that really works. Mineral, maybe, if you want to argue what he's made out of due to the Ground type.
What does Blissey's size have to do with anything? It's clearly a Fairy type creature, so it gets it.Gravity isn't so much of a stretch if fat-asses like Blissey get it.