Type: Bug/Poison
Classification: Poison Bee Pokémon
Height: 1.4m
Weight: 40.5kg.
Ability: Adaptability
The poison it produces from its four limbs all work instantaneously, yet the poison it emits from its tail is slow-acting. It uses the former to prevent its foes from fleeing, and the latter to deal the finishing blow. With six wings, Mega Beedrill attack a target with great speed. The poisonous barbs on its tail and arms both grow larger, and its legs sprout poisonous stingers to boot!
Mega Evolution gives Mega Beedrill a massive Attack and Speed stat boost. Its Adaptability ability increases the power of moves of the same type as the user from the standard x1.5 to x2.0. When used with a high accuracy, high power move, this Pokemon can deal devastating damage.
Reference and images: Serebii.net
Additional references, images, and information: pokemonrubysapphire.com
I think mega beedrill is the best