Gengar

Gengar returns for another bout in OU, still undisputed as one of the only Pokemon to consistently remain in the tier across all generations. It resists Fairy and can hit Fairy-types hard with its super effective Poison STAB moves, which makes it a very effective offensive answer to the likes of Mega Altaria, Mega Gardevoir, and Clefable, and the Steel-type losing its Ghost-type resistance makes it easier for Gengar to fit moves onto a set and harder to switch into it. Sadly, the presence of priority users, Assault Vest users, and powerful Mega Evolutions leaves Gengar struggling to keep up. However, Gengar's typing, ability, and support movepool let it act as a powerful stallbreaker, and its offensive stats and very good Speed tier don't let it down against offensive teams. A number of other traits, such as acting as a spinblocker and an effective Destiny Bond user, makes Gengar a rather consistent, yet still unpredictable choice for many teams.