Gengar (F) @ Life Orb
Trait: Levitate
EVs: 4 Def / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Shadow Ball
- Focus Blast
- Pain Split
- Substitute
Gengar counters Celebi pretty well in general. Celebi rarely has a psychic move and this set in particular doesn't, so Gengar can come in only fearing Hp Fire. Even at + 2 Hp Fire isn't going to do much to Gengar and Celebi is forced to either switch or prevent Gengar from getting a substitute. Gengar's Lo Shadow Ball OHKOs Celebi and may even be in position to get a large pain split or sub on the next Pokemon based on how that scenario plays out. I would personally go for the Sub, because there are more speedy threats in DW OU than the current BW OU.