Mega Beedrill

One of the first Mega Pokemon introduced to Pokemon Go, Mega Beedrill looks absolutely terrifying with its high ATK stat. While Bug and Poison typings are typically not as valuable as other typings, the early accessibility makes it a good entry option. It should be noted while Mega Beedrill packs a big punch (or sting), it's also very fragile and likely won't last long as an attacker. Stronger Bug-type Mega Pokemon will likely be introduced in the future to replace Mega Beedrill, but for now this is a cool addition to any player's collection. Also worth noting is that Mega Beedrill packs the highest Poison DPS of any of the Mega Evolutions, to the point where its Poison moveset actually out-damages its Bug moveset, though Poison is still a less than useful type in raids generally speaking.

Best PvE Offensive Moveset

• Bug Bite* and Infestation have roughly similar performance, with Infestation having better damage and Bug Bite better energy gain, though the legacy Bug Bite pulls ahead just slightly. 
• Poison Jab with Sludge Bomb is actually Mega Beedrill's strongest moveset by a fairly wide margin. Poison Sting falls behind.
• X-Scissor is fast and furious, giving Mega Beedrill a bug type set.
• Don't bother with any non-STAB options for Mega Beedrill.