Poisons and Potions:
Poisons and potions in B.T.L. are simulated using a container for your substance. You won't actually have anything in the container, but you must act as though you do. You can use bottles, vials, whatever you like. The substance doesn't have to be a liquid. It could be in powder form. Powders can be carried in small packets, jars, or poison rings. If someone asks you what is in the container, you can lie. If someone asks to analyze what's in the container, provided he has any authority to do so, you must tell what it is. Or stab them with your poison dagger and run away.
Poisons and potions, depending on the type, may be applied to items. You just have to come up with a reasonable explanation of how you accomplished it.
If you want to add a few drops of poison to someone's wine, you must open your bottle of poison, pretend to pour the poison into their glass of wine, and put your poison bottle away with out anyone noticing. If your victim drinks the wine, you must then tell them what effects they are experiencing. Or you could have someone else tell them. A Pooh-Bah would be a good candidate for giving the happy news. That makes it much harder for the victim to guess who the culprit is, or if there is a culprit. They could be getting ill... mysteriously ill. It couldn't possibly be your fault. How could they suspect such a thing? You don't have to admit to poisoning them; out of game, they will probably suspect you, but in-game they have to go by their character's perception of the situation.
Poisons and potions can be natural, alchemical, or magical. It doesn't really matter how they are created; they work the same way. You can find an herb that causes hallucinations, create a potion that causes hallucinations, or magically enchant some water to cause hallucinations. If you can get someone to take it, they will experience hallucinations.
You have to have alchemy skills to create poisons or potions. You have to be a magic user to enchant poisons or potions. But you don't need to be anything except sneaky and quick of hand to trick someone into taking one.
Potions can be beneficial, too. Medicines are potions. You can buy potions from the local apothecary. Possibly from the Mages Guild, also. A couple of healing potions in your pocket can come in handy.
Common substances used for poisons and potions will be listed in the appendix, right after the magic spells. If you are playing a character with poison or potion lore, check with the Pooh-Bahs for the game supplement with more advanced knowledge and special techniques. If you are a magic user, check under spells, or run your ideas past the storytellers.