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From Terraria Wiki
Land Mines are unique Hardmode, post-Plantera placed items. They remain dormant once placed, until a character touches them or they are activated by Wire, at which point they explode, dealing 250 damage. They are purchased from the Demolitionist for 5 each, after Plantera and at least one Pirate Invasion have been defeated. In the Console version, Land Mines can be purchased before Plantera is defeated, but only at night; once Plantera is defeated, they will be available at all times.
- A Pressure Plate wired to Explosives may be more effective during PvP, since it is not as visible.
- Since the mobile version doesn't have a housing menu, Land Mines are useful for moving NPCs to different houses (NPCs sell different items in different biomes).
- Land Mines can be used as a way to kill (and collect drops from) friendly NPCs.
- In singleplayer, if a Softcore character is killed by a Land Mine, they will not drop money on death. This is because it counts it as a PvP death (also true for Hellfire Arrows and Explosive Bullets).
- The Land Mine's texture is a reference to "Worms", a series of video games created by Team17.