A mushroom poner! She sells mushrooms, and sometimes gives them for free if she likes you or if she's in the right mood. The problem is they're like Poison Joke, except with completely random effects. Will you grow twice as big? Change genders? Invert your colors? Turn into Twilight Sparkle? Become bio-luminescent? Grow a pair of bat wings? Turn into a monster? Nopony knows! Thankfully no matter what the effects only last 60 minutes, and they have a really nice savory umami flavor :D