Hydregion is a great option, imo! -
- Normal - Shiny
Psychic Moves: Zen Headbutt, Rest, Reflect
Nicknames: Renegade, DeathEater, Dementor, Pythagoras, Hydragon, Disastrous
Oh, and I just wanted to put my answer down, lol. Please don't rage at me. I think Hydregion matches all of your standard requirements and is totally black. That came out wrong :P And it has a great movepool. Same with FS, I don't know what "Pure Dark" means, so I have guessed what it is and have posted this answer, tell me to add anything if you need it. Hope I helped! And can you please define; "Pure Dark", please?