The magic mushroom theory is based on the idea that the figure of Santa Claus, as we know him today, was inspired by the use of hallucinogenic mushrooms in ancient winter solstice celebrations.
According to this theory, the red and white colors of Santa's attire, as well as the tradition of leaving gifts, are all derived from the use of magic mushrooms in ancient pagan rituals. The theory suggests that these rituals were a way for people to connect with the spirit world and communicate with their ancestors, and that the figure of Santa Claus evolved over time to become the jolly, gift-giving figure we know today.
There is little concrete evidence to support this theory, and it remains largely a matter of speculation. However, it is certainly possible that the use of hallucinogenic mushrooms played a role in the development of the Santa Claus myth, as the use of psychoactive substances has been a part of many cultures throughout history.
Overall, the magic mushroom and Santa Clause theory is an interesting and unique way to look at the origins of the Santa Claus myth, but it should be noted that it is just one theory among many and has not been widely accepted by scholars.