Gengar

Mega Gengar is able to maintain a valuable niche in the Uber tier with Shadow Tag, which allows it to trap and remove foes. This makes Mega Gengar, albeit situationally, a stallbreaker, wallbreaker, and revenge killer rolled into one. Its excellent Special Attack and Speed stats aid it in this role, as do utility moves such as Taunt and Destiny Bond. Gengar's defensive typing along with its initial ability Levitate grants it three immunities, allowing it to come into battle a bit more easily. However, Mega Gengar's paltry bulk does it no favors, especially in an offensively inclined metagame. It is also susceptible to Pursuit, although this can be circumvented with the appropriate moves. Mega Gengar is often forced to sacrifice itself with Destiny Bond if it wishes to remove a healthy threat, and it faces indirect competition from other Mega Evolutions. It is worth noting that losing Levitate lets it absorb Toxic Spikes upon switching in and that it is able to spinblock, two small but situationally useful traits.