I've been running max Atk Assault Vest Snorlax with rock slide and it's a very solid volcarona counter. Bulky Volcarona does nothing to it and even max Sp Atk life orb fails to 2Hko at +1. It can always switch in on a quiver dance and beat it.
Snorlax @ Assault Vest
Ability: Thick Fat
EVs: 176 HP / 80 SDef / 252 Atk
Adamant Nature
- Pursuit / crunch
- Rock Slide
- Earthquake
- Body Slam / return
+1 252+ SpA Life Orb Volcarona Bug Buzz vs. 176 HP / 80 SpD Assault Vest Snorlax: 185-218 (36.6 - 43.1%) -- guaranteed 3HKO after Stealth Rock
+1 0 SpA Volcarona Bug Buzz vs. 176 HP / 80 SpD Assault Vest Snorlax: 108-127 (21.3 - 25.1%) -- 98.9% chance to 4HKO after Stealth Rock
252+ Atk Snorlax Rock Slide vs. 0 HP / 0 Def Volcarona: 452-536 (145.3 - 172.3%) -- guaranteed OHKO
252+ Atk Snorlax Rock Slide vs. 248 HP / 252+ Def Volcarona: 300-356 (80.4 - 95.4%) -- guaranteed OHKO after Stealth Rock