Camerupt @ Cameruptite
Ability: Solid Rock
EVs: 248 HP / 252 SpA / 8 Def
Modest Nature
- Fire Blast
- Earth Power
- Hidden Power [Ice]
- Will-o-Wisp
252+ SpA Mega Camerupt Hidden Power Ice vs. 252 HP / 116+ SpD Flygon: 300-356 (82.4 - 97.8%) -- guaranteed 2HKO after Leftovers recovery
0 Atk Flygon Earthquake vs. 252 HP / 4 Def Mega Camerupt: 216-254 (62.7 - 73.8%) -- guaranteed 2HKO
So it might seem that Flygon wins. But no! Burn them on the switch or after their first EQ, and bathe in the glory of this:
0 Atk burned Flygon Earthquake vs. 252 HP / 4 Def Mega Camerupt: 108-127 (31.3 - 36.9%) -- 75.8% chance to 3HKO
And then you can finish them off with a move of your choice.
It really doesn't matter that Camerupt uses two moveslots for this; it has the last two practically free, anyway. This set allows you to lure the grounds that threaten you, and then top 'em off with some unexpected HP Ice.
Oh and of course, U-Turn does nothing.