Death barrier

The Death Barrier or Death Plane is a special type of floor, which causes Mario to lose a life if he is above it and vertically too close to it. It is analogous to the bottomless pits of previous games. A floor is used for this case since Mario cannot inhabit any region without a floor triangle underneath him, as that is considered Out of Bounds.

The death animation usually triggers well above the physical height of a Death Barrier, presumably to avoid Mario falling onto it and standing there. However, it can be downwarped to or stood upon during a Power Star cutscene, and Mario's shadow is still visible on the surface of the Death Barrier, as with any other floor.

Several objects, such as Goombas and Scuttlebugs, have special programming in place to despawn them if they reach the Death Barrier, to prevent them from walking around on top of it. In the case of the Mystery Goomba, it only exists for one frame as it spawns at the Death Barrier and consequently despawns as soon as possible.