I dunno. True, Mega-Charizard Y has very good Special Attacking sets (ie: Flare Blitz + Special), but I've been burned by more than just those attacks. I've seen Charizard-Y with Earthquake and even Dragon Pulse and Air Slash on the switch-in which puts a major dent into Chandelure. Besides, I've got to wait a bit and see whether Charizard X or Charizard-Y comes out, and wait a bit more to see whether Y is Mixed or Special-based.
If you're expecting "Standard Charizard-Y", guess what? Chandelure doesn't just "check" the set, he walls him. Your typical Fire Blast / Solar Beam / Focus Blast / Roost Charizard-Ys are all straight up walled, and Chandelure can take his sweet time 2HKOing Charizard Y. Instead, your focus is to maximize the amount of damage on the obvious switch-out.
252+ SpA Chandelure Fire Blast vs. 4 HP / 0 SpD Mega Charizard Y in Sun: 143-168 (47.9 - 56.3%) -- 87.5% chance to 2HKO
If you expect a `mon that is faster than Chandelure, use Overheat -> Switchout. Otherwise, use Fire Blast and try and 2HKO any fool who switches into Chandelure.
Now... if you're expecting Physical Charizard-Y (Earthquake is sometimes run to beat out Heatran), Chandelure never really had a safe switch-in to begin with.
I'm not kidding when I say Overheat is the best option. Its a simple and conservative play that takes advantage of your opponent's Drought, the obvious switch-out (since stanard Charizard-Y is fully walled), and maximizes the damage done to your opponent's best move.
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EDIT: Getting Choice-locked into a 60-BP Rock attack seems like a terrible idea to a pursuit-weak / ghost-weak pokemon. Its like you're inviting Aegislash or Bisharp to just own you...