Glitched tiles are special tiles that are not originally included in the game, but can be created by code editing. Typing any symbol another than tileset codes to the map data's tile code and loading the level will result in a "5" tile that appears harmless, but acts strangely when touched. Sometimes it works like a bounceblock, while sometimes it kills the ninja.
Glitched tiles have also been used in mapmaking, though extremely rarely. In these cases, to have the desired effect, the map must usually be cleared in the Debug Mode by pressing "J" before playing, or to avoid random deaths, press "1" before playing. A good example of using glitched tiles in mapmaking would be Jiggerjaw12358's "Glitchtastic" -DDA series.