The experienced fungophagi tell that if skin the classic toxic fly amanita (red mukhomor) and boil it three times for several hours, every time replacing the water, they get totally edible.
This leads to the conclusion, that actually it's the only edible forest mushroom at all.
Because it's hard to confuse it with anything else, it for sure is toxic, and the recipe makes it edible.
While gathering other, presumably edible mushrooms, you never can be sure if the tasty leccinum scabrum (aka "underbirch mushroom"), which you just have picked up, is not actually a tylopilus felleus (aka "fake underbirch mushroom").