Cactus

An unused cactus can be found within the game files of Super Mario 64, loaded in memory with Shifting Sand Land. It was likely intended to be used in the outside area of Shifting Sand Land as a decorative or hazardous object, but went unused due to unknown purposes.

Cognitive Irrational Fear
Despite many players not having any fear of cacti or other sharp objects, the cactus' existence creates a level of unease and fear in these players. These very same players insist that this cactus appeared when they played Super Mario 64 and lunged at the player. Then they would report to have nightmares about touching cacti.