When the shaman went out to gather the mushrooms, he would wear an red outfit with either white trim or white dots, in honor of the mushroom’s colors. And because at that time of year the whole region was usually covered in deep snow, he, like everyone, wore tall boots of reindeer skin that would by then be blackened from exposure. He’d gather the tree-dried fly agarics and some reindeer urine in a large sack, then return home to his yurt (the traditional form of housing for people of this region at that time), where some of the higher-ups of the village would have gathered to join in the solstice ceremony.
But how would he get into a yurt whose door was blocked by several feet of snow? He’d climb up to the roof with his bag of goodies, go to the hole in the center of the roof that acted as a chimney, and slide down the central pole that held the yurt up over the fireplace. Then he’d pass out a few ‘shrooms to each guest, and some might even partake of some of the ones that had been hung over the fire. Clearly, this idea of using the chimney to get in and pass out the magic mushrooms (and other goodies) had sticking power. Interestingly, even as late as Victorian times in England, the traditional symbol of chimney sweeps was a fly agaric mushroom — and many early Christmas cards featured chimney sweeps with fly agarics, though no explanation of why was offered.
http://www.endalldisease.com/magic-mushrooms-and-the-origin-of-christmas-is-santa-a-mushroom/
http://inhabitat.com/santa-and-the-shrooms-the-real-story-behind-the-design-of-christmas/