Charizard-Mega-Y @ Charizardite Y
Ability: Drought
Level: 50
EVs: 252 HP / 116 Def / 20 SpA / 84 SpD / 36 Spe
Modest Nature
- Flamethrower / Fire Blast
- Solar Beam
- Hidden Power [Ice]
-
Earthquake
0- Atk Mega Charizard Y Earthquake vs. 252 HP / 0 Def Heatran: 136-160 (68.6 - 80.8%) -- guaranteed 2HKO after Leftovers recovery
It comfortably 2HKOs with no risk of missing. Heatran in retaliation can Lava Plume for less than 25% or Toxic but little else.
I've used this myself a fair amount on Naganadel teams to lure and weaken Heatran among other things.
Most of the details don't matter, EQ is the important bit, but the EV's for this one survive a 252+ Salamence DEdge and KOs back with HP Ice (15/16 to KO vs 4/0). Also Survives Koko Tbolt if there's no boosting item and OHKOs that with Sun Flamethrower.