Take my advice (like Jeff is saying) Houndoom is fast, but it won't stick around for long. You've best bet is giving it Faint attack, rather than Thunder Fang, or Fire Fang, but you should really have Faint attack.
So instead of Nasty Plot, Faint Attack
And maybe Will-Owhisp instead of Thunder Fang, or Crunch...You should go for high speed, fire attack, or Heat Wave is a good one too.
Oh! Or a Sludge Bomb!
With Houndoom's speed and Spatk, a Sludge Bomb plus Faint Attack would be a leathal combination
Nature: Impish, Quirky, Haughty...I think
Items: Sharp (Quick) Claw, Charcol, Dark Shades/Sunglasses, Fire Plate, Shadow Plate or whatever its called