The Ethereal Pedestrians powerup causes all pedestrians in the level to became translucent and untouchable. Their transparency makes them harder to see, but there is no point in seeing them at all, because they can't die or get injured. At least Immortal Pedestrians can still provide some fun by being pushable and such, but ethereal pedestrians can't be touched at all. However, they can still die in other ways rather than getting run over, such as falling off a cliff or drowning.