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Topaxci
From Discworld & Pratchett Wiki
If a shaman successfully powders up and inserts into various orifices the mystic mushroom, partakes of the sacred toadstool, smokes sufficent of the holy rhizome, then whilst sitting crosslegged under a pine tree is not distracted by blue four-sided triangles pin-wheeling accross his visual field , and can prevent the top of his head from unscrewing and drifting away, he may then see the god Topaxci. This earns him the name of Shaman.
The god is also known as Topaxi (after some red mushroom, this is close enough,) god of certain mushrooms, and of "great ideas that you forgot to write down and will never remember again", and some other things. He is featured in a painting by Paul Kidby as published in The Last Hero. See also: The Light Fantastic

