Invisibility Potion is a potion that makes the drinker invisible.
Mildred and Maud make this potion by mistake in their first year, when they are supposed to be making a Laughter Potion. The same potion is used by the frog-Mildred used to turn invisible in A Bad Spell For The Worst Witch. This was also the potion used by Agatha Cackle and her coven to try to sneak into the Academy. When taking invisibility potion, you disappear instantly, but reappear gradually, starting with the head, then the rest of the body and finally the feet. Seen in A Mean Halloween, Double, Double, Toil and Trouble, and Its a Frogs Life.