For this troll you need any pickaxe, which is pretty easy to get, a redstone torch, something a little bit harder to get, and an actual friend, which is the hardest thing to get in this short build. If you managed to find one of his/her iron doors with a pressure plate in front, get your pranking pants ready!
Break the iron door.
Dig two blocks down from the block where the iron door used to stand.
Obviously, you need to then get out of the hole you’ve made.
Cover the hole with a block any block.
Step on the pressure plate to update the iron door.
Because the iron door is powered, it gets locked. Whenever your friend steps on the pressure plate, it won’t open.
When your victim destroys the iron door then tries to fix it by placing it back on the same spot, it will stay open due to still being powered by the redstone torch.
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