Would like to add lonely Houndoom since it's able to trap Rotom trying to voltswitch out of Pursuit. It's by far my favorite version of mixed Houndoom.
Houndoom @Back Glasses/@Life Orb
Ability : Flash Fire
Lonely
EVS: 252 ATK / 252 SPEED /6 SPATK
Crunch
Pursuit
Sucker Punch
Overheat
Garchomp does not get swords dance here. Toxic gets alot of use to punish rotom-w switching in or trying to defog.
Careful Exca makes more sense with a bit of SpD and speed invest but I prefer jolly, keep the moveset and give it 252 speed.
Otherwise that's a solid team that will bring you success on the ladder.