This little fella right here:
Talonflame @ Choice Band
Ability: Gale Wings
EVs: 252 HP / 252 Atk / 4 SpD
- Brave Bird
- Flare Blitz
- Steel Wing
Thick Fat obviously doesnt work with Flying moves, so Brave Bird would be x2.
Talonflame x4 resists Grass, and MVenu usually only carries Grass STAB.
252+ Atk Choice Band Talonflame Brave Bird vs. 252 HP / 0 Def Mega Venusaur: 392-464 (107.6 - 127.4%) -- guaranteed OHKO
note: that is the usage set for MVenu, if it has 252 Def, this is the calc:
252+ Atk Choice Band Talonflame Brave Bird vs. 252 HP / 252 Def Mega Venusaur: 320-380 (87.9 - 104.3%) -- 25% chance to OHKO
guaranteed 2HKO with a chance to OHKO, pretty good.