Actually Gastrodon takes a hefty amount of damage in the sun (see the calcs above), and can be OHKOed if it switches into Overheat two times after Stealth Rock damage, and this is assuming that it has max investiment in SpD. Also, about the dragons that resist Overheat: 52SpAtk Choice Specs Rotom (Neutral) Overheat in Sun vs 4HP/0SpDef Leftovers Salamence (Neutral): 80% - 94% (266 - 313 HP). Guaranteed 2HKO. (an OHKO after Stealth Rock) 252SpAtk Choice Specs Rotom (Neutral) Overheat in Sun vs 252HP/0SpDef Leftovers Dragonite (Neutral): 57% - 67% (221 - 261 HP). Guaranteed 2HKO. (Assuming that Multiscale is broken, even Dragonite won't like the damage that it's going to take from Overheat in the sun) 252SpAtk Choice Specs Rotom (Neutral) Overheat in Sun vs 4HP/0SpDef Leftovers Levitate Hydreigon (Neutral): 74% - 87% (242 - 285 HP). Guaranteed 2HKO. (Sadly, Hydreigon is neutral to Stealth Rock, wich means that it has to switch 2 times into it to actually instantly die, but nonetheless it is not going to survive the second blow) 252SpAtk Choice Specs Rotom (Neutral) Overheat in Sun vs 252HP/0SpDef Leftovers Levitate Latias (Neutral): 48% - 56% (176 - 207 HP). Guaranteed 3HKO. 12% chance to 2HKO with Leftovers. (I think that I don't need to make the calcs with Latios, right?) 252SpAtk Choice Specs Rotom (Neutral) Overheat in Sun vs 36HP/0SpDef Leftovers Haxorus (Neutral): 98% - 115% (297 - 349 HP). Guaranteed 2HKO. 90% chance to OHKO. 252SpAtk Choice Specs Rotom (Neutral) Overheat in Sun vs 4HP/0SpDef Leftovers Haxorus (Neutral): 101% - 118% (297 - 349 HP). Guaranteed OHKO. (Haxorus, wich resists Overheat, is OHKOed in the sun without Stealth Rock. Even 36 HP EVs versions of Haxorus only have 10% chance to survive - if Stealth Rock is off the field) Tyranitar in fact laughs at Overheat but hates being hit with Volt Switch repeatedly: 252SpAtk Choice Specs Rotom (Neutral) Volt Switch in Sandstorm vs 252HP/176SpDef Leftovers Tyranitar (+SpDef): 18% - 22% (76 - 90 HP). Guaranteed 6HKO. Tyranitar sets without investiment in SpDef may hate having to switch on Volt Switch so many times. As for partners, I think that due to the sheer power of Overheat in the sun, the only partner that it really needs is Ninetales. But as Tyranitar is still a threat, something like Dugtrio or Terrakion may be a cool partner for Rotom-W. Venusaur of course makes an amazing partnership with Rotom-H, as it destroys all Water-types that laugh at Volt Switch and can defeat the dragons with Sludge Bomb/Hidden Power Ice. Also, before somebody says that Rotom-H is outclassed by either Heatran or Victini, Rotom-H has some advantages over them. Over Heatran, Rotom-H is immune to Ground, has STAB Electric-types so it's not helpless against bulky Water-types, has Volt Switch to mantain momentum and has Trick to surprise those pink blobs. Over Victini, Rotom-H is not weak to Pursuit, it's STAB doesn't lower its defenses and speed, thus not making Rotom-H as prone to revenge killing as Victini, receives STAB on the Electric-type attack and is not going to take as much damage from hazards as Victini due to immunity to Spikes.