There are different sets for gengar you know :)
The one I used was the special sweeper set, while most others are physical/special walls.
The life Orb does come in handy, raising attack power by 30% at the cost of 10% of HP
But you didnt realize you were battling someone who has used gastly and its evolutions since generation 1. I think if it wasnt for the fact that I use them so much I would have definately not been able to knock it out. Ive never used the life orb before so I learned how useful it can be!