New Team

Alright, so I'm starting my Soul Silver over in order to make another team to battle my friend with. This will be our third time planning out a team for the soul purpose of battling each other, and this time around I don't know who to take. So far I am planning to use Gengar (my favorite pokemon), Swampert, Mothim, and Houndoom. What are some good pokemon to fit the remaining spaces? Also if you think another pokemon would better fit the role of the ones already listed, feel free to share.
Thanks!

My current plan is as follows:

Gengar:
Item:Big Root
Ability: Levitate
Moves: Hypnosis, Dream Eater, Thunderbolt, Shadow Ball

Mothim:
Item: Choice Scarf
Ability: Swarm
Moves: Bug Buzz, Air Slash, Fly, Hidden Power

Houndoom:
Item: Life Orb
Ability: Flash Fire
Moves: Sucker Punch, Pursuit, Fire Fang, Thunder Fang

Swampert:
Item: Leftovers
Ability: Torrent
Moves: Hydro Pump, Ice Beam, Earthquake, Roar (this move is only here because I am considering running a pokemon with stealth rocks and causing and want a way to force a switch so they are forced to take the rocks damage)

Again any help would be greatly appreciated!