Since you àre almost at the end of the game, I will suggest Weavile to you. . Weavile does fit your conditions for Types as well as Attacking. Additionally, it has great 120 Attack and 125 Speed. It also gets a solid Dark Type STAB in Night Slash as well. It also gets Ice Punch as solid STAB. For coverage, it gets X-Scissor, Brick Break and Poison Jab. With these moves, it covers Molayne (Partially), Kahilli, Acerola and part of Hau's Team. It is available at Mt. Lanikala.
Weavile @ Black Glasses
Poison Jab/Swords Dance