Gengar

Gengar is an interesting Pokemon. It gets a wonderful movepool with super effective coverage and sacrificial moves that can hurt pretty much anything the OU tier has to offer. However, since Shadow Ball is physical, Gengar gets no special STAB moves to run off that amazing base 130 Special Attack stat. Gengar is also very frail, and while its Ghost typing is very useful for capitalizing off foes that only run Normal-type STAB moves, it's vulnerable to Pursuit and cannot take a hit that it doesn't resist. Moreover, as a Ghost-type, Misdreavus outclasses it as a spinblocker, Perish trapper, and Snorlax counter because of Gengar's unfortunate weaknesses to Earthquake and Starmie's Psychic. Furthermore, its Speed, while great, is eclipsed by that of Raikou and Starmie, which leads to particularly relevant match-up problems. In spite of these issues, Gengar is the tier's best assassin, being able to take down pretty much anything it wants to with Explosion, Destiny Bond, wonderful type coverage, or some sort of surprise. To get the most out of it, Gengar users should be sure to play to its strengths, maintain good prediction, know how to utilize the element of surprise, and be wary of letting it take any kind of status-inducing move or unresisted hit.