How are these heads sharing the specs?
Item: Choice Specs
EVs: 252 SpAtk, 252 Spd, 4 HP
- Dark Pulse
- Earth Power / Dragon Pulse / Draco Meteor
Dark Pulse is your main STAB attack, Flamethrower removes Steel and Ice types and is boosted in Sun, Surf handles Fire types and Ground types. Earth Power offers some nifty coverage, while Dragon Pulse gives you a secondary STAB and way to fight back about Dragons that is reliable, and Draco Meteor is your classic Dragon type nuke.
It has a ton of coverage with its huge movepool, so this is easier said than done. Any faster Dragon should be able to down Hydreigon, so start with that. Mantine resists a lot of his moves, and has the bulk to handle what does hit it and threaten it back with Ice Beam. Chansey and Blissey shut Hydreigon down just like they do any other special sweeper. Yanmega, Ninjask, and Accelgor all have the speed to outrun and smash Hydreigon with their STAB attacks. Toxic and Thunder Wave are great for shutting him down.
This is a signature that doesn't eat up an absurd amount of space.