Rotom-Wash @ Waterium Z
EVs: 252 HP / 252 SpA / 4 SpD
IVs: 0 Atk
- Hydro Pump
- Volt Switch
- Hidden Power [Ice]
Rotom-W takes both of Heatran's STAB to the face without a hitch and is bothered even less by its common coverage moves barring Bloom Doom, which is rare. Rotom-W is also a pretty splashable poke that can glue a lot of things together by being a deterrent to extremely popular pokes like Landorus-T, Gyarados, Tapu Fini, Hippowdon and Celesteela to name a few.
252+ SpA Rotom-W Hydro Vortex (185 BP) vs. 212 HP / 156+ SpD Heatran: 224-266 (116 - 137.8%) -- guaranteed OHKO
252 SpA Heatran Fire Blast vs. 252 HP / 0 SpD Rotom-W: 45-53 (28.6 - 33.7%) -- 0.4% chance to 3HKO
252 SpA Heatran Flash Cannon vs. 252 HP / 0 SpD Rotom-W: 16-19 (10.1 - 12.1%) -- possible 9HKO
Heatran Earth Power vs. Levitate Rotom-W: 0-0 (0 - 0%) -- aim for the horn next time
The only thing you really have to watch out for is Bloom Doom Heatran, which can be easily baited out anyway.