Minecraft wiki entry for Defense, associated text: Another effective trap against enemy players is sometimes known as the "KILL" land mine. Place an upwards-facing dispenser, filled with splash potion of Harming VII, surrounded by pressure plates. This is most effective if there is a ceiling above, so that the player can't run or walk out of range as easily. However, note that splash potion of Harming VII cannot be obtained without item spawning (in multiplayer) or mods. What you can do is use a lower Harming potion that is obtainable in survival, but it won't kill the player instantly.