If held by a Beedrill (or is present in the player's BagPE), the Beedrillite allows it to Mega Evolve into Mega Beedrill if its Trainer has a Key Stone. A Trainer can only Mega Evolve one Pokémon per battle (or only have one Mega-Evolved Pokémon at any given momentZA).
As a Mega Stone, it is unaffected by item-negating effects (such as Embargo and Klutz). Item-manipulating effects (such as Trick and Fling) cannot give or remove a Beedrillite from Beedrill.
Outside of battle
If held by a Beedrill, the Beedrillite allows it to Mega Evolve into Mega Beedrill when it performs a Spectacular Talent during a Pokémon Contest Spectacular if its Trainer has a Key Stone. Beedrill will remain a Mega Beedrill until the Talent Round ends.
Erases Pokémon and disruptions around a spot you tap. Erases nine tiles in a square shape surrounding each spot. Does not activate if the foe is defeated. Only gives 3 seconds to tap. Can choose not to erase any. The disruption countdown formerly did not decrease if this effect was triggered by the first match of the combo, but this was corrected in Version 1.3.28 (3DS)/1.9.1 (Mobile).
In PS616, Giovanni was revealed to have obtained a Beedrillite. He used it to Mega Evolve his Beedrill as part of his explanation that the meteoroid threatening to destroy the world may be housing a Pokémon inside of it.
