Minecraft wiki entry for Combat, associated text: During thunderstorms, if lightning strikes close enough to a creeper, it becomes charged. Charged creepers are one of the most dangerous mobs in the game, with it's close range explosion dealing so much damage that a player with full diamond armor enchanted with Blast Protection IV is left on just 2 hearts. However, the lightning also damages the creeper, making it a faster kill if the player decides to attack it. Just make sure it doesn't explode and they should be able to kill it just like normal creepers.