Stop the Knightmare
From the Super Mario Wiki
Stop the Knightmare is the second to last main mission in Luigi's Mansion: Dark Moon. It is the boss mission of Treacherous Mansion, where Luigi must defeat the Tough Possessor in order to get the final piece on the Dark Moon.
Luigi ends up in a room with 5 suits of armor, one having the Dark Moon piece on it, Luigi attempts to get the piece right before the Tough Possessor scares Luigi, and tries to destroy Luigi by using the suits of armor in the room by cloning itself.
To defeat the Possessor, Luigi needs to trip all the armor on carpets to make them fall, causing the Possessors to combine into one and bash a wall, once two skins are removed, he and the clones make a giant suit of armor in order to crush Luigi.
To defeat the giant suit of armor, Luigi has to make sure both feet are on two carpets and lift them both, but this requires good timing. Once done, Luigi can defeat the Possessor and get the Dark Moon piece.
Luigi then gets a call on the Dual Scream from Gadd, who tells him to come back, but when Luigi is being pixelated back to the Bunker, he is warped back to the portal, only the piece remains, making E. Gadd horrified.
The portal on the Terrace is still open, but we've got to hurry. Button up those overalls, my boy! It's time to battle King Boo!
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