Gengar

By virtue of its great coverage and natural power augmented by Sheer Force and Life Orb, Gengar is one of the better wallbreakers in Almost Any Ability, and one that is not dead weight against more offensive teams thanks to its great Speed tier. Gengar also has access to a great support movepool including moves such as Taunt and Mean Look, which help it do its job as a Sheer Force wallbreaker and Normalize attacker. Gengar's Ghost typing gives it utility as a spinblocker, making it a good fit on offensive entry hazard-stacking teams, and an important immunity to regular Normal-type Extreme Speed, allowing Gengar to revenge kill Pokemon such as Tough Claws Lucario. However, it also makes Gengar weak to Pursuit and Knock Off, the latter of which being quite popular. Very low bulk makes Gengar vulnerable to faster attackers and the enormous amount of priority in Almost Any Ability, and it means that, if Gengar does not KO the foe, it will most likely get KOed itself. Additionally, the Normalize set is quite useless if Gengar does not get a chance to use Skill Swap. Last but not least, Gengar faces competition from Doublade and Aegislash as an offensive Ghost-type because they have more bulk and resistances, but Gengar is faster and more threatening to bulkier builds.