In traditional fantasy RPGs, a wizard can pre-cast a spell into a magic item for one-time use, typically as a potion or a scroll. Only Magic-Users (and maybe Thieves) can cast spells from scrolls. Anyone can gulp down a potion. Based on tables of magic items from the original texts, there are certain spells that go on scrolls and others that go in potions.
One argument made is that potions are meant to produce an effect on the imbiber rather than some effect directed outward. This explanation thins a bit when it comes to potions of control, e.g. a Potion of Undead Control. In 3E, it’s possible to brew a potion of any spell 3rd level or lower, which means a Potion of Fireball is feasible. Drinking and spitting fire seems very natural and evocative, so I’m going with it. Here’s how it works.
We have a flask. It’s warm to the touch. If you pop the cork, a small flame dances out from the mouth of the flask. If you pour it out or break the flask, you just get some lamp oil. If you drink it, it burns going down, just link chugging a flask of whiskey. And it wants to come back up immediately, but you can try to keep it down. If you let it come right back up, a fireball bursts from your mouth, exactly as the spell cast by a Magic-User of level 5 – 20.
If you want to hold it down, make a save versus magic. If you make it, it stays in your belly for up to a turn. If you fail, it comes right back. When you want to produce a fireball, make another save versus magic. If you fail, the fireball projects from the other end of your digestive system, probably exploding at your feet.
If successfully belched up, a fireball shoots a stream of fire of a hundred feet or more until it explodes at the point where the potion drinker intends.
Yeah, yeah, game balance. This does not particularly concern me, especially since I’ve got three high-level fighters in my long-running campaign that each have girdles of giant strength which allow them to throw boulders every round. If one of them has an accident with a potion of fireball, it will be worth it.