A trap with which you can kill someone by luring them. If you step on the pressure plate, you fall down together with it.
First, you build yourself a house of your own choosing.
Then you put a pressure plate in front of the door.
Underneath is a sand block. Under the sand block you put a TNT block. Underneath there should be a deep shaft -> at least 10 blocks deep.
If your opponent now comes across this little house, he will think that it is something to spend the night in. So he steps on the pressure plate, knowing that the door will open. But the TNT block comes loose and he falls with it into the depth and falls.