This is my first contribution to smogon, so I hope that I've got something useful to share.
[SET]
name: OrbGar
move 1: Trick
move 2: Taunt
move 3: Shadow Ball/Venoshock
move 4: HP Fire/Focus Blast
item: Toxic Orb
ability: Levitate
nature: Timid
evs: 4 HP/252 SpA/252Spe
(IVs for HP Fire if needed, otherwise 31 in all, except for Attack)
[SET COMMENTS]
1)Trick works well on Gengar, thanks to its vast movepool, speed, and unpredictability.
2)Toxic orb cannot poison Gengar, as it is poison typed itself. Gengar can also bluff a choice item with this set.
3)Can totally wall Chansey and Blissey thanks to Taunt (Chansey/Blissey cannot heal themselves by Natural Cure either)
4)Venoshock has 195 BP after an opponent being poisoned with STAB.
[ADDITIONAL COMMENTS]
5)EVs are for Gengar to hit max speed to take out Timid Latios
6)This set requires a good amount of prediction, if Steels switch in on Trick, they'll only lose their item.
7)Hence, HP Fire is used to get most steels running for cover.
8)Focus Blast and SB has excellent 2-move coverage, and Venoshock has insane power.
9)This set is vulnerable to Tyranitar, who can force Gengar out using Dark moves or Thunder Wave. Gengar can only return a Focus Blast, which does not OHKO Tyranitar in sandstorm

[SET]
name: OrbGar
move 1: Trick
move 2: Taunt
move 3: Shadow Ball/Venoshock
move 4: HP Fire/Focus Blast
item: Toxic Orb
ability: Levitate
nature: Timid
evs: 4 HP/252 SpA/252Spe
(IVs for HP Fire if needed, otherwise 31 in all, except for Attack)
[SET COMMENTS]
1)Trick works well on Gengar, thanks to its vast movepool, speed, and unpredictability.
2)Toxic orb cannot poison Gengar, as it is poison typed itself. Gengar can also bluff a choice item with this set.
3)Can totally wall Chansey and Blissey thanks to Taunt (Chansey/Blissey cannot heal themselves by Natural Cure either)
4)Venoshock has 195 BP after an opponent being poisoned with STAB.
[ADDITIONAL COMMENTS]
5)EVs are for Gengar to hit max speed to take out Timid Latios
6)This set requires a good amount of prediction, if Steels switch in on Trick, they'll only lose their item.
7)Hence, HP Fire is used to get most steels running for cover.
8)Focus Blast and SB has excellent 2-move coverage, and Venoshock has insane power.
9)This set is vulnerable to Tyranitar, who can force Gengar out using Dark moves or Thunder Wave. Gengar can only return a Focus Blast, which does not OHKO Tyranitar in sandstorm