Hydreigon isn't trash right now. Only Fini, Clef, and Chansey switches in effectively on LO 3 Atk + Roost. Hydreigon gets free switches against locked Gengar, A-Marow, Ferrothorn, Pex, Skarm, locked Gren and many others. It teams well with MegaGross. With Phero out its viability will go up...