Alchemy; as simple as I can make it and have a system that is still loosely playable.
All Potions require 4 things;
1. An Oil (1 item slot, provides adjective)
2. A Powder (1 item slot, provides noun/verb)
3. A Catalyst (1 item slot, provides tone + potency)
4. Alchemical Equipment (1 encumbrance slot)
All things can be reduced to either Oils or Powders by use of Alchemical Equipment. These substances produce a single, unchanging effect based on what they were derived from. At its simplest, Oils provide an adjective effect and Powders denote a particular verb or noun. A single Oil and a single Powder are combined to create a potion, the effects of any potion are the combination of the Adjective and Verb/Noun.
For example, an amateur adventuring alchemist slays two Blink-Dogs and reduces one into an Oil and the other into a Powder using his alchemical equipment. Using his Alchemical Equipment, he is aware of the effect the Blink-Dog Oil and Blink-Dog Powder will bring to any particular potion. (These effects are improv’d by the DM)
Blink-Dog Oil = Capricious
Blink-Dog Powder = Teleport
Having discovered these effects, he (and the DM) log the effects into a codified alchemical grimoire for future reference. Before the Alchemist can make his Capricious Teleport potion (drinking this potion will cause random teleportation), he must select a Catalyst. Catalysts are rare and collectable magical artifacts that allow and modify the synthesis of potions. Catalysts dictate the Tone and Potency (and flavour) of the Potion. (the effect of Catalysts are known only to the DM)
The Alchemist only has one Catalyst, A Hand of Glory, a Catalyst of medium potency that makes potions Gothic. It takes 4 hours to distil a potion, but when complete the potion is recorded as 'Potion of Capricious Teleport (Hand of Glory)’. The Catalyst used, means that this Potion will last for 10 minutes and each teleport will be accompanied by a cloud of black, sulphurous vapour and an almost silent screaming sound.
Oils and Powders are used up during potion distillation. Catalysts (unless specified) remain unconsumed
Alchemical Equipment is never consumed.
Potions only ever have two ingredients, 1 Oil and 1 Powder.
Unless very large, most creatures or objects can only be reduced into a single batch of a single ingredient.
Oils and Powders weight 10-20 coins.
Alchemical Equipment weighs 100-150 coins.
Catalysts can come in any shape or size, 1 coin – immovable.
Exploitation of Mundane Substances:
If players attempt to use incredibly mundane substances (like grass) in their potions, allow them. However, reduce the potion’s Potency by one step and think very carefully about what effects the Oil and Powder will give. The effects should be niche, dull and not terribly useful. Also consider the large quantity of the mundane substance the players would have to gather in order to produce an effectual yield of oil/powder. Grass for example may yield;
Grass Oil = Wilt/Wilting
Grass Powder = Grass
Potion Potency is derived from the Catalyst used to distil the potion. The DM ultimately rules for how powerful any potion is. However, as a guide, assign Catalysts a level; weak, medium or powerful. A Catalyst’s Potency is known only by the DM and is for players to work out, as with a Catalyst’s Tone.
Some potions have instantaneous effects while other would work for a duration, take this into account when assigning potion effects. It would be best practice for the DM to record specific potion effects for consistency.
Potency levels could be used thusly. Weak potions last from 1 combat round to 10, Medium potions last for 10 minutes to an hour. Powerful potions last anywhere between one day and a month. Some potion effects would be instant, Catalysts would affect this too. Damage is assigned thusly, weak Catalyst = 1d4, powerful = 1d20 and medium; any die in between. Anything else (such as if a potion effects or creates a volume of something) would be up to the DM’s discretion.
On Catalysts and Tones:
Catalysts come in many forms. They are special things (or even places) that make the potion work – something vaguely magical or extraordinarily masterwork, something that could theoretically hold, move, stir or affect the potion in some way can be a Catalyst. Catalysts are often bespoke, predefined items. Players shouldn’t be able to pull out a troll’s fang or an orc’s finger and convince the DM it is a Catalyst. Catalysts should be rare. They should be something heard about in rumours; not bought in a shop.
Examples of Catalysts could include things like a Unicorn's Horn, a Cursed Alchemist's Ladle, an Elven Gossamer-Funnel, an Angelic Drinking Chalice ... an Atlantean Whisk? An entire dungeon could be a powerful Catalyst, with a chute or trough running from one end of the dungeon to the other. Pour the potion in one end and collect the finished potion from the other.
Tone descriptors derived from Catalysts are words that affect how a potion's effects manifest. Sloshing a potion of Capricious Teleport through an Elven Gossamer-Funnel might make it Ethereal. So, the random teleportation that happens when the potion is imbibed is slow and ghostly, it takes 1 round to ‘complete’ a teleport, during this time an astral image of the teleporter is seen floating through the air towards the sight where they will emerge from their random teleport.
It’s trickier to improv in the moment but if a potions flavour (Gothic, Ethereal) can have a potential gameplay effect, all the better. For example, a Gothic teleport leaves smoke and a smell, an Ethereal teleport is still random but can be more predictable.
Interesting Catalyst modifying words could be Hot, Cursed, Hideous, Alien, Hallucinatory, Bizarre, Light, Aggressive, Wild, Heavenly and so on, any word that is evocative to you, Tone could even be several words if you find that easier. The player won’t know and can only intuit Tone based on their experimentation.