Battle Moveset

A Good Moveset for Houndoom would have to be this:

Attacks:

Sunny Day
Solarbeam
Flamethrower
Crunch

Items Attached:

Leftovers

Preferred Nature:

Timid

Strategy Using Houndoom

A standard moveset, probably used by many and you will come across people with counters to this. This works well with Houndoom's special attack and speed, although its defenses aren't that great. So, if you need to, set up Sunny Day and use Solarbeam, and it should also increase the strength of its Fire moves too. Flamethrower and Crunch for STAB, Crunch can also reduce your opponent's special defense.
Like most dark pokemon, Houndoom is a dual type, meaning it has weaknesses which can be exploited, such as water type moves, rock, ground etc. The two abilities Houndoom can learn is: Early bird and Flash Fire. I would pick Flash Fire over Early bird, although I doubt anybody would be stupid enough to attack Houndoom with a fire move, but Flash fire boosts the fire type moves that Houndoom uses.

EV Corner:

Max out the EVs in Speed & Special Attack for Houndoom with any remaining in Hit Points

Strategy Against Houndoom

Houndoom has Average Defense and above Average Special Defense so your best bet with this is to pummel it with Super Effective attacks such as Water or especially fighting and Houndoom will be toast

Contest Moveset

A good Contest Moveset for Houndoom would have to be this for the Cool Contest best with Lonely, Adament, Naughty or Brave Nature:

Attacks:

Hyper Beam
Sunny Day
Solar Beam
Double Team

Items Attached:

Red Scarf

Strategy Using Houndoom

If you do the attacks in this following order you should have very few problems; 1st - Sunny day, 2nd - Solarbeam, 3rd - Double team, 4th - Solarbeam, 5th - Hyper beam

Locations in Games

Ruby/Sapphire Trade from C/FR/LG Colosseum Realgam Tower Fire Red/Leaf Green Evolve Houndour

Animé Appearences

Houndoom has had a few Animé Appearences. First it helped Togepi get back to Misty when it became lost after a battle with Team Rocket. After that the Iron Masked Marauder had one and used it to try and get Celebi. After that Harrison used it to catch a Sneasel AND to battle Ash in the Silver Conference.And finally Team Magma use it as one of their henchman Pokémon Episode 182: Houndoom's Special Delivery! Episode 205: The Screen Actor's Guilt! Movie 4: Celebi - Voice Of The Forest! Episode 261: Entei At Your Own Risk! Episode 267: Pop Goes The Sneasel! Episode 273: Playing With Fire! Episode 274: Johto Photo Finish! Episode 278: A Ruin With A View! Episode 303: A Three Team Scheme!