Gengar

Ghost

With high Speed and Special Attack, Gengar serves as an effective revenge killer, wallbreaker, and cleaner for Ghost. Choice Scarf Gengar's excellent Speed tier allows to outrun most of the unboosted metagame as well as most other Choice Scarf users. Gengar's Poison typing also comes in handy for absorbing Toxic Spikes against Poison and Water teams as well as putting heavy pressure on types such as Fairy. Gengar has a colorful movepool with coverage options such as Thunderbolt for Mantine, Trick for disabling walls such as Chansey and Zapdos, and Destiny Bond to lure and remove certain targets that threaten Ghost, such as Alolan Muk and Bisharp. Gengar is very, very frail, however, and is easily taken out by Pokemon that it cannot KO first. Its low defenses also leave it checked by strong priority users such as Scizor and Azumarill. Gengar is very vulnerable to Pursuit trappers such as Alolan Muk and Mega Aerodactyl, the former of which can switch in on any of Gengar's attacks and take it out consistently. Despite high Special Attack, the relatively low power of Shadow Ball and poor coverage of Sludge Wave as STAB attacks limit what Gengar can check effectively.

Poison

Gengar's high Speed and Special Attack make it an effective revenge killer and late-game cleaner, especially for Poison teams seeking an edge in the Psychic matchup. Its varied movepool gives it good offensive coverage and options to hit most switch-ins for significant damage, such as Focus Blast to hit Heatran. It can also cripple checks such as Chansey and Zapdos with Trick. However, Gengar's moves are individually easy to check, so locking it into one with Choice Scarf can give opponents undue momentum, and Gengar's frailty means it has few opportunities to switch in and leaves it vulnerable to any attacker that it cannot KO first, although a Normal immunity can be useful to force Diggersby into mind games. In addition, Gengar faces competition as a revenge killer from Nihilego, which offers useful defensive utility with a unique Flying resistance as well as handy STAB coverage for pressuring Flying teams.