Drasil

From berserkers on the battle field to wild ecstatics in mystery cults, the idea of being 'ridden' by the gods has followers throughout the world. This condition requires not only a means of accessing the Godmind as some call it, but also rigorous preparation of the body and spirit. Though a random ecstatic can sometimes get away with less than pure behavior, the experience is always better when a person abides by the bans and taboos set forth by their gods, and those who do not have an extremely unpleasant experience when they enter the Drasil state.
Godmind is a reference solely to the ecstatic state, which some practitioners of magic use to travel the Veil or Otherworld and others use to commune with the gods directly but never invite their interference. Drasil is different because in that state, a god actually 'rides' the practitioner, often enabling superhuman feats while the practitioner's body moves in the waking world. Berserkers are the most notorious of these, for while mystery cults are a worldwide phenomenon, they're almost universally accepted as part of the status quo and as the name implies the rites and practices of each aren't well publicized. Berserkers on the other hand have been seen on battlefields throughout the world and its history, with similar means of achieving their state. The berserker tradition in the far north is the longest-lived, and their tradition is also the best studied.
A potent mushroom grows in the region that is quite poisonous to humans (though some still risk ingesting its pure form), though reindeer can consume it and the necessary element of the mushrooms is then passed in their urine. Those who deride berserkers refer to them as 'piss-drinkers', though almost never to their face. While some shamans can ingest the mushrooms and dampen the effects on their own health, similarly producing this potent urine, the end result is the same and most berserkers use urine as an ingredient in their own beverages (low quality mead and herbs or honey to mask the flavor), quaffing it before battle. Despite their reputation as fearless savages as likely to kill their own people as the enemy, most berserkers live apart from society, seeking isolation to better commune with their gods and the spirits who occasionally ride them. Strong flavored foods and meat tends to be avoided as much as possible to make a purer vessel; berserkers who don't abide by these rules often get incredibly sick after the possession has ended.