Gengar has great Sp. Atk and Speed, while Crobat has low attack.
It has Cursed Body, and Mega Gengar has Shadow Tag, one of the best abilities. It learns many amazing moves, such as Will-O-Wisp, Hex, Sludge Bomb, and Taunt. Also it fills the role of stallbreaker, wallbreaker, and revenge killer in a team.