Breloom@Life Orb
EV's: 252 Attack/252 Spe/4 Def
Trait: Technician
Jolly Nature
-Spore
-Mach Punch
-Bullet Seed
-Drain Punch
Breloom has personally always given me problems and one of the pokemon that this variant of M-Gyarados has trouble with is indeed the Mushroom Pokemon. There really isn't much that needs to be explained since everything is standard for the most part so I'll post the calcs:
252 Atk Mold Breaker Mega Gyarados Waterfall vs. 0 HP / 4 Def Breloom: 89-105 (34 - 40.2%) -- guaranteed 3HKO after Stealth Rock
252 Atk Mold Breaker Mega Gyarados Crunch vs. 0 HP / 4 Def Breloom: 89-105 (34 - 40.2%) -- guaranteed 3HKO after Stealth Rock
252 Atk Life Orb Technician Breloom Bullet Seed (3 hits) vs. 0 HP / 4 Def Mega Gyarados: 444-522 (134.1 - 157.7%) -- guaranteed OHKO
252 Atk Life Orb Technician Breloom Mach Punch vs. 0 HP / 4 Def Mega Gyarados: 237-281 (71.6 - 84.8%) -- guaranteed 2HKO
252 Atk Life Orb Breloom Drain Punch vs. 0 HP / 4 Def Mega Gyarados: 296-351 (89.4 - 106%) -- 31.3% chance to OHKO
Here are the 3 scenarios:
1. Gyarados attacks right off the bat. Breloom takes that 34-40.2% damage and can either Mach Punch twice or Bullet Seed or it can Drain Punch for the possible KO and recover health.
2. Gyarados could set up a DD while Breloom comes in and follow up with 51.3 - 60.5% of damage, but will go down to the combo of Drain Punch+Mach Punch or double Mach Punch if you're paranoid about flinch hax
3. Gyarados sets up a Substitute while Breloom comes in and Gyara loses through the previous scenarios.