Fingerprick Cloning (5e Trap)
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Pricks you finger, sends your DNA to a mad scientist who clones you and you need to fight yourself.
When you attempt to picklock a locked door, a smal blade comes out and you must make a Dexterity (Slight of Hand) saving throw of DC 15 or else your pointer finger gets cut off and is teleported to another dimension. There is no damage. A long time down the road, you find out that, using your finger, a scientist has cloned you and there is now an evil version if you that tries to kill you. That version of you is the same level as you were when your finger was cut off.