The Poison Mushroom in the Super Smash Bros. games is the only item borrowed from another series whose appearance does not stay true to its original franchise. In the Mario series, poison mushrooms have distinct colouring from other mushrooms, but in the Super Smash Bros. series, they look similar to Super Mushrooms in order to purposefully confuse players. The differences between the two items are nearly unnoticeable - the Poison Mushrooms are only slightly less red and have a meaner look.
Contributed by CuriousUserX90