>>23029414252+ Atk Adaptability Mega Beedrill Poison Jab vs. 0 HP / 4 Def Mega Charizard Y: 260-308 (87.5 - 103.7%) -- 25% chance to OHKO
252 Atk Adaptability Mega Beedrill Poison Jab vs. 0 HP / 4 Def Mega Charizard Y: 238-280 (80.1 - 94.2%) -- guaranteed 2HKO
252+ Atk Adaptability Mega Beedrill Poison Jab vs. 0 HP / 4 Def Mega Lopunny: 224-264 (82.6 - 97.4%) -- 25% chance to OHKO after Stealth Rock
252 Atk Adaptability Mega Beedrill Poison Jab vs. 0 HP / 4 Def Mega Lopunny: 204-242 (75.2 - 89.2%) -- guaranteed 2HKO after Stealth Rock
I really wouldn't bank on a 25% chance and if you're using Beedrill chances are it has prior damage, which Jolly still KOs with.
Jolly Lopunny also outspeeds Adamant Beedrill, so just loses there.