>>15834153A Pokémon with 400 BST should be evolving rather than Mega Evolving, megas would be more fitting in stuff like Electabuzz, Porygon2 and the like. And Murkrow isn't that fully-evolved like. It is a small crow with a witch hat.
Mawile should have evolved as well, and giving said evo an additional Mega would have made Huge Power unneeded, and solve the HP problem.