Making a team of dark and psychic

[Ben Marsh]

Houndoom: Nasty Plot, Flamethrower, Dark Pulse, Hidden Power Grass. Modest Nature
Umbreon: Wish, Toxic, Protect, Heal bell. Sassy nature.
Skuntank: Haze, Taunt, Explosion, Sucker Punch, Jolly nature.

That should be a decent little addition to any team.  

[Imorinod]

Ben Marsh has the right idea.
A Houndoom with Nasty Plot will be one tough enemy.
I'm speaking from experience here.