>>22459384+2 252 SpA Solar Power Mega Houndoom Solar Beam vs. 92 HP / 0 SpD Azumarill in Sun: 996-1172 (273.6 - 321.9%) -- guaranteed OHKO
+2 252 SpA Solar Power Mega Houndoom Fire Blast vs. 4 HP / 252 SpD Eviolite Chansey in Sun: 435-513 (67.7 - 79.9%) -- guaranteed 2HKO
+2 252 SpA Solar Power Mega Houndoom Dark Pulse vs. 248 HP / 252+ SpD Palkia in Sun: 262-310 (68.4 - 80.9%) -- guaranteed 2HKO after Leftovers recovery
+2 252 SpA Solar Power Mega Houndoom Dark Pulse vs. +1 252 HP / 4 SpD Slowbro in Sun: 662-782 (168 - 198.4%) -- guaranteed OHKO
+2 252 SpA Solar Power Mega Houndoom Fire Blast vs. 4 HP / 0 SpD Salamence in Sun: 466-549 (140.3 - 165.3%) -- guaranteed OHKO
+2 252 SpA Solar Power Mega Houndoom Fire Blast vs. +2 252 HP / 252 SpD Sableye in Sun: 306-361 (100.6 - 118.7%) -- guaranteed OHKO
So, if weather was buffed to be better, M-Houndoom could 2HKO Sp. Defensive Palkia, Chansey, and M-Sableye, and OHKO M-Slowbro AND M-Salamence, provided 1 turn of set up. There is NOTHING you can switch in on it. Your only option is to revenge kill it.
Either that, or there should be a Special DDance that raises speed and Sp. Atk by one stage each, making it an unstoppable force even still.