The screen fades to black and an animation of a strange monkey-like Aztec-Paracas style drawing constantly cycling through various "states" very quickly is played along with a lively synth beat. Unsuspecting players are likely to be taken aback by the sudden explosion of vibrant color that stands in stark contrast to the bland hues of the Wilderness area. The animation continues until it is dismissed by the player.
The BGM that plays on the Aztec Rave Monkey's encounter is also played in the Teleport Maze at 50% speed.
There are numerous instances of Mesoamerican imagery blended with postmodern art styles throughout the game, including the KALIMBA TV channel, the Nexus' floor pattern, the paintings in Mural World, and various parallax backgrounds (such as the ones of Shield-Folk World and Eyeball World) of which the Aztec Rave Monkey is probably the most popular.
This recurring theme in Madotsuki's dreams may be a result of the Nazcan-style carpet pattern in her room - one of the few sources of visual stimulation in her waking world.
It is possible that KIKIYAMA selected this theme as it is a relatively 'alien' art style in most cultures and is therefore an effective way to demonstrate the bizarre nature of dreams to the player, and is also a flexible visual tool that can be seen as either intimidating or humorous depending on the nature of the image and the context of the environment. He could be based off of the Aztec monkey god Ozomatli, who is a god of song, dance, and drinking.
For more information, see Mesoamerican Imagery.