Mosquitus

Mosquitus is the giant bug mini-boss in Mega Man X3. It only appears if Vile is destroyed. X can destroy it, but if you battle it with Zero, X can gain the Z-Saber. But this also results in Zero being out for the rest of the game, and also results in the less ideal of the two possible endings. If Zero beats him, the monster will catch him in a death grip and explode.