While Beedrill isn't the best Bug-type sweeper with a Mega in NatDex Monotype, it's a good one. So here's a
somewhat viable moveset for Beedrill.
Beedrill-Mega (M) @ Beedrillite
Ability: Sniper/Adaptability
Tera Type: Poison
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Drill Run (great coverage, high crit ratio is very useful)
- Knock Off/Throat Chop (coverage for Ghosts that resists your STAB)
- Poison Jab (great STAB, assuming 140-160 BP with Adaptability)
- U-turn/X-Scissor ( U-turn for fast pivoting, X-Scissor for power.)
Jolly Nature is to ensure Beedrill outspeeds most other equally fast Megas, like Mega Sceptile.
252 Atk Adaptability Beedrill-Mega U-turn vs. 0 HP / 0 Def Tyranitar-Mega: 240-284 (70.3 - 83.2%) -- guaranteed 2HKO
Beedrill can also put some fully offensive Tyranitar (252 ATK, 252 SPD) in trouble.
Throat Chop is to stop Throat Spray Torch Song Skeledirge, while Knock Off is a great utility move, doing double damage on Pokémon with items.