Fake door

Trapdoors (also known as Fake Doors) are special traps designed to resemble real doors, and they are encountered during the events of Luigi's Mansion. They are placed throughout Luigi's Mansion to confuse and injure Luigi during his quest to rescue his brother Mario. If the green-clad plumber happens to turn the knob of a Trapdoor, the door springs open and flattens Luigi against the wall, causing Luigi to lose ten HP (and a few Gold Coins). A ghost can be heard giggling after Luigi is smashed. Sometimes, a trail of conveniently placed Gold Coins leads straight to a Fake Door to catch Luigi off-guard.

To determine if a door is real or fake, Luigi can check his Game Boy Horror. Real doors appear on the map, while trapdoors don't. Additionally, Luigi can vacuum a door with his Poltergust 3000. If the door rattles, it is real; if the door does not shake, it is a trap. Another way to tell if a door is real or fake is to look for a doormat under it. If there is a mat, the door is real. In some cases, however, a real door like the fortune teller's room does not have a mat either. Another way to tell if the door is a fake is when Luigi walks past a fake door, he glances at it as he walks by. Luigi does not look at doors if they are real.

The only way to defeat a Trapdoor is to set it on fire. The door then goes up in flames and disappears. Real doors do not catch on fire. However, if Luigi enters two different rooms and returns, the Trapdoor reappears.

It should be mentioned that in the blackout, the ghosts who are having a field day in the mansion increase the amount of trapdoors (like trapdoors leading to the storage room, projection room, and kitchen if they were real).