Minecraft wiki entry for Creeper_farming, associated text: To operate, the farm requires a creeper-only farm connected to a storage system. As creepers spawn, they are put into minecarts, which prevents them from despawning and removes them from the mob cap. These creepers are then stored, and when a thunderstorm hits, these creepers will be unloaded (because minecarts will be destroyed by the lightning) in a tight area, and the player can throw a Channeling trident at an armor stand with sky access, and the lightning will charge all creepers in the process. These charged creepers are now loaded in minecarts again, and can now be stored until further notice. A nearby regular mob farm that produces zombies, skeletons and creepers can now be connected to the charged creeper storage, enabling mob head farming.