Add a system of “hell curses”. When you enter a demon lord’s lair, you are afflicted with 2 random curses, which stick around forever until the lord is killed or bribed off.

You can receive at most six curses over the course of the game, requiring you to defeat the lords of the first three lairs you encounter. Further generation of lairs does not add any curses.

A non-comprehensive list of potential curses is:

• healing potions heal only half as much HP
• your speed is knocked down by 2
• your AC is deducted
• your spellcasting failure rates increase
• you are randomly inflicted with confusion every 50 turns or so

Exempt the healing-potion-on-Pestilence interaction from doing a roll versus monster MR, because in practice his MR is so high that it means healing potions are useless.

A formula to provide diminishing returns on the HP growth you get from potions, which is currently unbounded.

In the formula, X represents the total amount of extra HP points you would have in vanilla (1 per blessed healing, 5 per blessed extra healing, etc), R represents the actual amount of extra HP points you will have under this formula, e is Euler’s number (a constant), and A represents the desired asymptotic upper bound of extra HP points you will approach:

R = (2A / (1 + e^(-2x/A))) - A

The value of A is up to the designer. If it’s selected as 100, for instance, total HP gains from potions will get closer and closer to 100 as more and more potions are consumed, but the hero will never quite reach it.

Each Rider has the ability to use their attack to destroy items you’re carrying that are antithetical to their purpose, which replaces their normal attack.

• Death destroys amulets of life saving.
• Pestilence destroys all types of healing potions.
• Famine destroys horns of plenty and food items.

All of the healing potions heal a slightly variable fraction of your max HP, with some reasonable minimums and maximums, in order to keep healing and extra healing relevant beyond the early game. Proposed quantities are:

• Healing: 8/6/4 HP minimum, 10-20% of max HP, 100 HP maximum
• Extra healing: 16/12/8 minimum, 20-30% of max HP, 160 HP maximum
• Full healing: 100% of max HP, 400 HP maximum

Dipping a spellbook in any healing potion will restore one of its read charges. Dipping it in a potion of restore ability will restore all of its read charges. In either case, the potion is used up.

Occasionally, when generating a level 6+ spellbook, set its opoisoned flag to true. You get “The book was coated in contact poison!” not as a random spellbook reading failure effect, but when you try to read a book whose opoisoned is set to true. Triggering the contact poison usually (but not always) clears the opoisoned flag, so it won’t be poisoned if you try to read it again.

Dipping a poisoned spellbook in any healing potion will neutralize the poison and use up the potion. Possibly, dipping it in a potion of sickness will poison the book, though this would be useless unless monsters read spellbooks.

Buff healing potions to be more useful in a true emergency scenario, possibly making them rarer in the process. The problem with NetHack’s healing potions as compared to something like the cure wounds potion in DCSS is that they’re ineffective enough that the best thing to do is stash them away rather than actually using them as an emergency healing item.

Potion of elixir, which heals more HP than healing, but less than extra healing. It also recovers the same amount of Pw and restores 1 ability point in all attributes. HP and Pw maximums do not get raised.

Nerf the effects of diluted potions in order to disincentivize diluting them and fix alchemy abuses. Start with healing potions: a diluted healing potion of any type heals only half as much as otherwise, and either confers half as much max HP as an undiluted potion or possibly no max HP at all. When alchemizing with diluted potions, half of the amount dipped will bubble or steam off as water, wasting those potions entirely (e.g. 6 diluted healings + gain energy = 3 diluted extra healings).

Give potions more side dipping effects:

• Dipping an eroded item in a healing potion repairs erosion on it; 1 level for regular healing, 2 for extra healing, and 3 for full healing. Restore ability will repair all erosion as well.
• Dipping a negatively enchanted item in a restore ability potion reverts it to +0 if the potion is blessed, adds 1 point if uncursed, and does nothing if cursed.
• Dipping an enchantable item in a gain ability potion enchants it (by 1 point, always).
• Dipping an uncharged item (possibly excluding rings) into restore ability has the same effect as uncursed charging it. (Blessed charging cannot be reproduced this way, even if the potion is blessed).

Debilitating wound system that expands on wounded legs. Includes wounded arms and various types of disease and poison, all of which provide various debuffs. Quaffing any healing potion cures all of these at once on top of its usual HP healing.

Healing potions don’t give you different HP maximum increases depending on their beatitude any more. Instead, if they would have taken you above your maximum, your HP maximum is increased by that amount, to a maximum of +1 (healing) / +2 (extra healing) / +4 (full healing).