Heatran @ Leftovers
Ability: Flash Fire
EVs: 252 HP / 136 SpD / 120 Spe
Calm Nature
- Magma Storm
- Earth Power
- Protect
- Heavy Slam/Nature Power
While any Heatran set could, in theory, work here (modest scarf eruption/earth power is an OHKO, offensive 0-investment sets take 64-76% from Shadow Ball), a more defensive set gives potential longevity and increases Heatran's viability as a
check.
The EV spread here is the standard one running around in the calcs at the moment, with enough speed to outrun neutral base 60s (many of which could give Heatran a problem if they outspeed, but get smashed otherwise). The rest of the EVs are dumped into HP and SpDef. With this spread, Specs Blace's Shadow Ball does:
252 SpA Choice Specs Blacephalon Shadow Ball vs. 252 HP / 136+ SpD Heatran: 168-198 (43.5 - 51.2%) -- guaranteed 3HKO after Leftovers recovery
while Heatran's Earth Power returns:
0 SpA Heatran Earth Power vs. 0 HP / 4 SpD Blacephalon: 196-232 (79.3 - 93.9%) -- guaranteed OHKO after Stealth Rock
By no means can the Blacephalon afford to stay in on the Heatran; but, if it does, the Heatran can easily afford to Protect and gain Leftovers recovery. If the opponent switches to a passive mon like Blissey, their Protect won't be burned, and the Heatran can Protect again to gain an additional turn, if desired. While the Heatran remains healthy, the Blacephalon user is always on the back foot, as locking into a Fire move would be extremely risky.
Finally, this set incorporates the seldom-seen Heavy Slam tech. This pairs well with Protect in my opinion, since a Tapu Lele may come in on a <50% health Heatran and threaten it with Focus Blast. Protect allows you to scout this option and, if they predicted you to switch, you can stay in and OHKO even a Lele at full health. It also gives a more reliable option against Glowking, while Protect allows you to scout the Earthquake.
As one last note, this set also pairs well with Rillaboom since it doubles the Heatran's recovery while shielding it from weak Earthquakes. Nature Power therefore is an option in the last slot but, unless Swampert or others become common in the metagame, this probably isn't worth it.