Gengar

Gengar is a centralizing threat in ADV OU with amazing versatility. It boasts high Special Attack and Speed, which are both integral to its utility and offensive roles. In addition, one would be mistaken to assume that it is a glass cannon based on its poor defensive stats. It has immunities to Normal-, Ground-, and Fighting-type attacks and a resistance to Bug-type attacks, providing it with an abundance of opportunities to pivot in on mixed and physical variants of Salamence, Heracross, Snorlax, Swampert, Flygon, Gyarados, Aerodactyl, and Body Slam Jirachi. It even gets opportunities to pivot in on Toxic. Gengar also has very few weaknesses that aren't widely distributed, making its selection of checks highly specific.

One of Gengar's greatest assets is its ability to spinblock allowing Spikes to remain on the field. Another major boon to Gengar is its unique set of utility moves, which almost no Pokemon is completely able to shrug off; in particular, Will-O-Wisp severely threatens every non-Fire-type without Natural Cure, and even those that do get their recovery shut down by Taunt, making Gengar highly effective at pressuring passive Pokemon like Blissey and Milotic too. Offensively, Gengar's selection of coverage moves allows it to be an effective sweeper with Spikes support. As a dedicated Blissey lure, Gengar can even use Mean Look + Perish Song or Explosion in conjunction with Dugtrio, allowing specially offensive Pokemon to sweep.

While Gengar has many strengths, its propensity to be trapped, lack of STAB moves, and slight frailty hold it back. Pursuit Tyranitar OHKOes any Gengar that isn't properly EV trained to survive it. The lack of STAB moves but an abundance of coverage means that Gengar is not suited for consistently firing off strong neutral hits early-game, although it gets exponentially better with Spikes. Its low defensive stats can somewhat be compensated for through EV investment, but at the expense of a crucial amount of Speed.