[WildAce]

@ Kirean:
K, I agree with EQ > Dragon Claw for BellyZard (just ran all the numbers needed).

@ AMN:
Note that a little additional speed can come in handy in a Phazer vs. Phazer situation (not much really, a simple 20 Speed Evs should usually do the trick).
Also: Shed Shell is a VERY viable option over Lefties for escaping the likes of Magnezone.
Besides that: Whirlwind > Roar

@ Dark`: Please feel free to help out if you see anything wrong.
Remember, all help is accepted.

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GENGAR:

Gengar @ Life Orb
Ability: Levitate
Nature: Naive
Evs: 252 Speed / 136 ATK / 120 Sp.ATK
- Hypnosis / Focus Punch
- Thunderbolt
- Shadow Ball
- Explosion

Gengar with Explosion. The Evs allow it to always OHKO any Blissey with Explosion should the need arise.
Focus Punch is there to handle the likes of TTar / Weavile on the switch if hypnosis's accuracy doesn't suit your style.

Gengar @ Life Orb / Black Sludge
Ability: Levitate
Nature: Timid
Evs: 252 Sp. ATK / 252 Speed / 4 HP
- Thunderbolt
- Shadow Ball
- Substitute/ Hypnosis
- Destiny Bond / Hypnosis

One of my personal favorite variants.
Hypnosis + Destiny Bond : Status and Kamikaze
Substitute + Destiny Bond: Guage and Kamakaze
Substitute + Hypnosis: Status and Guage (safest version)
Those are your three options for the last 2 move slots.
What you choose depends on what function you want Gengar to serve.

Gengar @ Choice Specs
Ability: Levitate
Nature: Timid
Evs: 252 Sp. ATK / 252 Speed / 4 HP
- Thunderbolt
- Shadow Ball
- Focus Blast
- Energy Ball / Psychic

Good 'ol Specs Variant.
Very straightforward.

Gengar @ Black Sludge / Choice Scarf
Ability: Levitate
Nature: Timid
Evs: 252 Sp. ATK / 252 Speed / 4 HP
- Thunderbolt
- Shadow Ball
- Hypnosis
- Will-O-Wisp

The "infamous" Double Status Gengar made popular in DP.
Basically, you Hypnosis something, and Burn the PKMN that switches in next.
If this is your starting PKMN, Choice Scarf is a viable option to get in that first Crippling Status move.

Originally Posted by Kirean616

Ive seen this on the boards. I forgot who.

Gengar@Focus Sash
Hasty / Naive
252 Sp.ATK/ 252 Speed / 4 ATK (I'm assuming)
252 ATK / 252 Speed / 4 HP
Counter
Destiny Bond / Explosion
Thunderbolt / Sucker Punch
Shadow Ball / Hypnosis

Use as your starter and pray that they have Weavile. Counter it and then Destiny Bond the next guy. Takes down one to two guys if your opponent has an offensive starter.

Hypnosis + Sucker Punch has it's merits as well, especially vs. a Faster PKMN (i.e. Weavile) that would be carrying a Focus Sash...

Basically, you Counter KO a PKMN. If it hung on with Focus Sash, you finish it off with Sucker Punch.
Hypnosis the next PKMN.
Explode on the Switched PKMN.