Bronzong @ Leftovers
EVs: 252 HP / 252 Def / 4 SDef or EVs: 252 HP / 216 Atk / 40 Def
Relaxed Nature (+Def, -Spd) or Brave Nature (+Atk, -Spd)
- Gyro Ball
- Substitute/Stealth Rock
A Bronzong able to survive a Flare Blitz by Darmanitan and then KO with Earthquake. Heatproof is actually a solid ability. As long as the foe doesn't have a Spikes up or you manage to switch in on an Earthquake, most foes will be unable to tell that you have Heatproof and not Levitate, even if they go at you with a Fire type attack. And since they usually figure you have Levitate and don't want to waste a turn testing if you do, you'll usually go through the game not getting a Ground type move directed at you. The EVs allow it to survive a Flare Blitz even after having put a Sub up. This means you get to KO the Darmanitan and not the other way around. I like using a Sub on the first turn to see if a foe is going to switch in with a Fire type (mainly Darmanitan). Of course, that is just me. If you aren't battling by my standard "No Stealth Rock" rules, then you'll probably be best off using the second set of Evs, Nature, and Stealth Rock over Substitute. That way you can get your rocks up. The first EV/Nature set is for use with Substitute. Second is for use with Stealth Rock. The Substitute set gives you a 2HKO vs. Darmanitan, and thanks to Sub being up, you are guaranteed to be the winner of that fight. With the second set, this is guaranteed to OHKO Darmanitan with Stealth Rocks up.
For both sets, sure you pretty much sacrificed Bronzong, but you took down a dangerous foe in doing so. The rest of the moveset is for if you don't run up against a Physical Fire type, but in my experience, I'll be facing a Darmanitan most matches.
Thanks to PB for running off the much needed damage calculations.