I was wondering one day, “Why are potions always effective, doing exactly what they’re supposed to do, no matter who is taking them, or how long they’ve been sitting around?” And so, I decided to make a fun little potion mishap table to make drinking the magical elixir in that little bottle a little bit more of a gamble. How often should this happen? Under what circumstances should a potion go bad? That’s for the GM to decide 
Potion mishap table, roll 1d10
- Effects wear off at inconvenient time
- Effects are difficult to control - Fire breath is always on, or resistance requires concentration to maintain, etc.
- Effects have obvious symptoms - water breathing gives you gills; giant’s strength makes your arms enormous!
- Effects are much stronger than expected - “can do a thing” becomes “needs/has to do a thing”; “can resist a thing” becomes “continually produces/radiates a thing” or “requires regular contact of the thing”
- Effects are accompanied by other minor magical effects - skin/eyes change color, digestion moves backwards, shadows deform or escape, magic runes appear on skin or above PC’s head, skin/eyes/mouth glows, etc.
- Effects are contagious - by touch or proximity
- Effects make it impossible or difficult to do something normally easy - ex. A potion of blindsight might make it difficult to stay in lit areas; a potion of cat’s grace might make it impossible not to chase mice; a potion of stone skin might make it impossible to swim.
- Has a different effect which begins with the same letter as the intended effect - ex “Cold resistance” becomes “calm resistance” - you are susceptible to emotional effects, or “Fire breath” becomes “fog breath” - PC can make a fog bank.
- Has a different effect which rhymes with the intended effect - ex. “Fire resistance” becomes “fire persistence”: fires on you cannot be put out! “Cure wounds” becomes “lure wounds”: enemies gain a bonus to hit you.
- Combine 2
