Just to add - There's another play style for gengar.
Gengar. Calm nature 252def & 252 sp.def 4hp;Toxic - Hex - Destiny bond (when you now your going down) - Protect
Works surprisingly well!
Here's a small list of Pokemon that work well with 252 and 252 with 4 ev.
- Electivire - jolly nature (Has strong attack anyway)
- Excadrill - (Yes somepeople use this) Adamant nature - Mold Breaker -
- Ferrothron - Defensive nature/ (not entirely preffered, cause of it's awesome def.)
- Talonflame - Priority bird (252 attack. Speed not a neccesitybecause of priority) except for needing it's flare blitz) others may suggest otherwise though :P.
- Mega Pinsir - Adamant nature is awesome with this.
- Charizard Mega X & Y -Jolly nature for X version and Timid for Y.. My preferred game style, they're strong enough without extra nature boosts) just my opinion.
- Diggersby 252 attack 252 speed
- Mienshao 252 attack 252 speed
- Medicham 252 attack 252 speed
- Flareon 252 attack 252 speed
- Raichu 252 special attack 252 speed
I've answered with experience, if you feel this is a wrong answer for the question provided, please just post a small comment and i'll --hide-- it.
Hope I Helped!