20 double-edged potions for the ingenious adventurer

I've written before about item-based problem solving in D&D, and the principle that creatively solving problems using whatever random junk you have lying around is always going to be more satisfying, and more memorable, than just beating them down with brute force. Magic items open up possibilities for all kinds of even more creative solutions, because they don't have to be limited by what's physically possible. But a magic item that grants a permanent new ability is likely to radically change the nature of the campaign.

One solution is to be generous in giving out one-use rule-changers, or 'potions' as D&D calls them. Plenty of things that would be game-breaking in a spell or item become perfectly viable if they can only be used once. But a good potion should be versatile: the kind of thing that could be used in all kinds of different ways, in all kinds of different contexts. No-one's ever going to be proud of the time they worked out that maybe they should drink a fire resistance potion just before fighting the red dragon. But beating a red dragon with a creatively-applied potion of levitation is the stuff of which gaming legends are made. 

Here's a list of twenty potions. All have been written with an eye towards OSR-style problem solving, and most of them are versatile enough that they can potentially be used in all kinds of different ways, including as weapons. Because why fight fair when you can cripple your opponents with potion side-effects instead?

Delivery system (roll 1d4)

1. Must be swallowed. (Have you considered dosing your enemy's food?)
2. Must be injected into the bloodstream. (Putting it on a sharp weapon and stabbing someone with it is sufficient.) 
3. Works on contact with skin. (Throwing the bottle at someone should work unless they're covered in heavy clothes or armour.) 
4. Gaseous: must be inhaled. (Throw it at your enemy's head!)

Effects (roll 1d20)

Roll	Effect	Beneficial uses	Hostile uses
1	Antigravity. User ‘falls’ upwards for six seconds unless something gets in the way.	Getting to hard-to-reach places on ceilings, overhangs, etc.	Six seconds of unimpeded reverse freefall will leave you 176 metres up in the air.
2	Hatemask. For the next 1d6 hours, the user takes on the appearance of whichever living being they most hate. (If the being they most hate is is a radically different size to them - e.g. a human who hates a dragon - they appear as a them-sized version of it, instead.)	Infiltrating the stronghold of your archenemy. Potentially a useful disguise if your archenemy is of a different gender / ethnicity / species to yourself.	Learning about your enemies. Revealing their secrets. Potentially getting someone killed by their own allies, by e.g. making someone look like ‘the enemy’ in the middle of a battle.
3	Nilbog essence. For one round, the user is harmed by healing and healed by harm.	Use it just before taking massive damage, e.g. walking through a wall of fire or jumping off a cliff.	Use on an enemy just before they get healed.
4	Soulfire potion. Magical flames burst from the user’s body, burning everything for 10’ around them for 1d6 minutes. During this time they are totally immune to heat and fire, though their equipment isn’t.	Protecting yourself from fire, or from being swarmed by enemies.	Breaking up enemy formations. Destroying someone’s equipment.
5	Beast-tongue. For 1d6 hours, the user gains the ability to communicate with animals. They lose the ability to communicate with any creature of above-animal intelligence.	Talking to animals.	Preventing someone from communicating with their allies, giving orders, etc. (Especially handy if used against summoners, who will be unable to command their summonations!)
6	Psychic sensitivity. For 1d6 hours, the user can detect the surface thoughts and emotional states of all nearby sentient beings by sight. Powerful emotions cause confusion and painful headaches.	Reading people’s minds.	Use it on someone in the middle of a riot or battle and watch them have a psychic meltdown.
7	Rust monster extract. For 1d6 rounds, every ferrous object that comes in contact with the user’s skin turns instantly to rust.	Rust your way through metal locks, barriers, etc. Destroy enemy weapons and armour on contact.	Use it on someone with metal weapons and armour and watch their equipment turn to rust.
8	Stoneflesh. User’s flesh becomes grey, heavy, and super-dense. For 2d6 minutes the user becomes slow, clumsy, and almost impossible to harm.	Endure damage. Survive dangerous environments.	Make someone too slow to catch you. Render finesse-based fighters ineffectual. Make flying creatures drop out of the air, or swimming creatures sink to the bottom of the water. Or use it on someone standing on a flimsy bridge or walkway and watch them fall through the floor.
9	Elixir of undeath. For 1d6 hours the user becomes pale and cold to the touch. They do not need to eat, drink, or breathe, and will register as undead to Detect Undead spells. Mindless undead will ignore them unless directly attacked. Sunlight is painful to them, holy water burns them, and they become vulnerable to Turn Undead.	Feigning death. Sneaking past zombies. Pretending to be a zombie. Navigating environments where breathing is dangerous or impossible.	Use it on someone and then get a cleric to Turn them, or douse them in holy water. Prevent someone from operating in bright sunlight. Get someone mistaken for a zombie and murdered by passing paladins.
10	Clawbrew. Causes the user’s jaws and hands to warp into huge, bestial fangs and claws for 1d6 hours, capable of inflicting terrible injuries. Clear speech and fine manipulation are impossible for the duration.	Scaring people. Boosting your unarmed combat capability.	Rendering someone unable to talk effectively. Preventing someone from carrying out delicate manual tasks (e.g. archery, lockpicking). Getting someone lynched as a werewolf.
11	Potion of photosynthesis. For 3d6 days the user’s skin turns green, and they are able to gain all the nourishment they need from sunlight and water. Lack of these things causes them to weaken and wither.	Subsisting without food. Pretending to be a Martian.	Use it on an underground predator and wait for it to starve to death.
12	Arctic Adaptation. Causes all temperatures to be experienced as 20C (36F) higher than they actually are for 3d6 hours.	Surviving ice and cold.	Use it on a warmly-dressed or armoured person on a sunny day and watch them pass out from heatstroke.
13	Gluesweat. For 1d20 minutes the user’s body exudes a sticky, gluey substance, making them stick to everything they touch unless they slowly and deliberately rip themselves away.	Use your glue-hands to climb along walls and ceilings like a spider.	Laugh as the feet of monsters stick to the floor, the arrows of archers stick to their fingers, thrown weapons stick to their wielder’s hands, etc.
14	Mistform. The user (and all their equipment) turns into a cloud of gas for 2d6 minutes. During this time they cannot move under their own power, but will move with the prevailing winds.	Turn to gas and get your allies to fan you through prison bars, across pits, etc.	Turn someone else to gas and fan them off a cliff, or into a box which you then lock shut, or just use it on someone in a strong wind and watch them blow away. Can also be used just to get rid of someone for 2d6 minutes.
15	Nighteye. For 2d6 hours the user can see perfectly in poor light, and dimly even in complete or magical darkness. Ordinary daylight is painful to them, and bright light is blinding.	Use it to see in the dark.	Use it on someone at midday or near a light source to blind them.
16	Gillbrew. The user grows gills, and for the next 3d6 minutes they can breathe underwater. They cannot breathe in air during this time.	Use it to breathe underwater.	Use it to force someone else to start suffocating unless they shove their head underwater.
17	Lightfoot. For 3d6 minutes the user’s mass is reduced by 90%, as is the mass of their equipment.	Balance on twigs, climb over damaged surfaces, make enormous leaps, carry someone bigger than you are.	Use it on someone, then shove them hard and watch them go flying. (Makes it much easier to push people into things!) Renders enemies largely ineffectual in physical combat.
18	Rubberflesh. For 1d6 hours the user’s flesh becomes stretchy and rubbery, allowing them to stretch their limbs 50%  further than usual. Their weird, rubbery flesh is hard to crush but parts easily beneath sharp edges, taking half damage from bludgeoning attacks and double damage from slashing attacks.	Stretching to get something just out of reach. Protecting yourself against crushing attacks.	Rendering enemies vulnerable to cutting attacks.
19	Slipperiness. For 2d6 minutes the user’s body becomes slippery and almost frictionless. If they are barefoot this requires them to move slowly and with great care to avoid slipping over with each step.	Slithering out of bonds, webs, etc.	Slowing barefoot enemies. Preventing people from following you up ropes, ladders etc. Making people’s tools or weapons slip from their hands. Making people lose their grip on ropes or ledges.
20	Magnetism. For 1d6 minutes the user becomes powerfully magnetic, attracting all nearby ferrous metals to them.	Stick to metal surfaces. Make an enemy’s weapons stick to you. Could also be used to suck metal objects out of pools, mud, pits, etc.	Make someone a literal magnet for arrows and other metal projectiles. Make someone’s own weapon stick to them. Make the weapons of their allies stick to them. Make a whole bunch of heavily-armoured opponents stick together in a big magnetic ball with the user in the centre. Point and laugh.