This article is from the 2006 series of SMBZ and is no longer canon.
Poison mushroom is a type of mushroom appeared in the Mario Series that power-downs the user of it. They can be found in "? blocks", "! blocks" and some brick blocks. It appeared in the 8th episode of Super Mario Bros. Z series, used by Basilisx. He threw 2 of them to Mario and one of it power-downed mario to super mario from hammer mario and one of them posioned him. Its unknown whether of not will appear again.