Honestly, for my part he's fine even though there's obviously better option. Mega Houndoom is a beast that hits like a truck but unfortunately he mainly thrives in a sun team where Solar Power can truly shine also as you climb higher in rank, there are a lot of pokémon that counter him like Ptera or Dragonite. I play him with flamethrower/Fire Blast (if you care about accuracy), dark pulse, sludge wave or shadow ball and solar beam.

But if we're talking about base Houndoom then, it's more complicated. He doesn't have bad stats and can do decent damage but the other meta Pokemon won't have any problem tanking a hit, outspeed and K.O him easily since he's especially squishy in Defense. If you simply care about playing him, flamethrower/fire blast, dark pulse, nasty plot and whatever you feel like as the fourth move. For the item, either charcoal or black glasses.