I need a good moveset for gengar.
I was thinking go all out offensive with:
shadow ball
dark pulse
psychic/hyper beam
thunderbolt/thunder

i was also thinking going defensive with:
hypnosis
confuse ray
destiny bond
shadow ball

what do u think i should have?

Gengar has wet-paper-like defenses, so if you want an all-out offensive set, try a Choice set:

Gengar@Choice Specs/Choice Scarf
252 SpA/252 Spe/6 HP
Timid Nature
Shadow Ball
Focus Blast
Thunderbolt
Trick

Shadow Ball and Focus Blast's combo are not resisted by anything, and Thunderbolt provides extra coverage. Trick to give your Choice item to something that doesn't want it.

Or, try this nice Focus Sash one:

Gengar@Focus Sash
252 SpA/252 Spe/6 HP
Timid Nature
Shadow Ball
Destiny Bond
Focus Blast
Thunderbolt

Attacks are the same as the last one, and Destiny Bond allows you to KO another Pokemon.

Hope this helped!