Chandelure@Assault Vest
Ability:Infiltrator/Flash Fire
EVs:196 HP/ 252 Def/ 60 Spe
Modest Nature
-Shadow Ball
-Flamethrower
-Energy Ball
-Clear Smog
This was the first thing that came to mind, and I hope I don't regret nomming it. Clear Smog is used to get rid of Suicune's boosts, w/ the EVs outspeeding it. Unfortunalely, this set only has a 10.9% chance to 2HKO 252/4 SpD Sicune, while always getting 2HKOd in return, but it can kill Suicune if it's asleep or something, and wiping boosts is it's main thing vs Suicune anyways. Chandelure is even better equipped to fight Blaziken, as many run STABs alongside HP Ice, which can't touch Chandelure-even if you go Infiltrator, Flare Blitz from 252 +Atk Mega Blaziken is a 3HKO, and you 2HKO it w/ Shadow Ball. Stone Edge from 252 +Atk Mega Blaziken is only a 2HKO, and it's liable to miss meaning Chandelure has a chance vs even variants of Mega Blaziken running Stone Edge(and according to the PGL, Stone Edge isn't in the top 10 moves for Blaziken anymore-though Rock Slide is andd is actually much more threatening to Chandelure thanks to higher accuracy, a flinch chance, and the fact that it's still a 2HKO.) Knock Off is also threatening, but few Blaziken run it. The reason I slashed Infiltrator and Flash Fire is because Infiltrator is better, but Flash Fire is more useful against Blaziken. This set also does some other neat stuff like surviving 252 SpA Mega Gengar's Shadow Ball and OHKOing w/ a Shadow Ball of its own.
Some defensive calcs for Blaziken and its Mega:
Mega:
252+ Atk Mega Blaziken Stone Edge vs. 196 HP / 252 Def Chandelure: 124-148 (77.5 - 92.5%) -- guaranteed 2HKO
+2 252+ Atk Mega Blaziken Flare Blitz vs. 196 HP / 252 Def Chandelure: 111-131 (69.3 - 81.8%) -- guaranteed 2HKO
252+ Atk Mega Blaziken Thunder Punch vs. 196 HP / 252 Def Chandelure: 47-56 (29.3 - 35%) -- 11.8% chance to 3HKO
Regular:
+2 252+ Atk Life Orb Blaziken Flare Blitz vs. 196 HP / 252 Def Chandelure: 117-138 (73.1 - 86.2%) -- guaranteed 2HKO
+4 252+ Atk Life Orb Blaziken Thunder Punch vs. 196 HP / 252 Def Chandelure: 147-173 (91.8 - 108.1%) -- 50% chance to OHKO
252+ Atk Life Orb Blaziken Stone Edge vs. 196 HP / 252 Def Chandelure: 133-156 (83.1 - 97.5%) -- guaranteed 2HKO
244 SpA Life Orb Blaziken Hidden Power Ice vs. 196 HP / 0 SpD Assault Vest Chandelure: 14-17 (8.7 - 10.6%) -- possibly the worst move ever