Ring of criticality, a charged ring that has an (enchantment)% chance per hit of changing the result of the die roll for that hit into a critical hit that deals double damage (and will trigger effects such as Vorpal Blade decapitation). If negatively enchanted, it has the same chance of changing the die roll into a critical failure that deals zero or 1 damage.

Helmet (or possibly blindfold) slot artifact named The Masque of the Read Death. Has some mechanic related to sickness.

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.

Implement a wizard mode command that freezes all monsters (done by blocking their normal movement point gain), which is useful for debugging.

Some monsters can block being detected by your telepathy, either innately (disenchanters, perhaps) or as a monster intrinsic conferred by armor (such as a tinfoil hat) or spellcasting by an ally. Also, possibly allow for area-of-effect “telepathy dead zones”.

Archeologists can apply their whips to cross over a ground-based trap with impunity, a la Indiana Jones.

Refactor to-hit mechanics into a simple 1d(attacker’s bonuses) versus 1d(defender’s bonuses) computation, where the attacker hits if their roll is higher.

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).

Rather than making weapons train 1-to-1 on all successful hits, make them train differently:

• Weapons train only when their natural damage die rolls a 1 / rolls a max (ignoring other weapon damage bonuses), so that weaker weapons train faster than stronger ones, and weapon skill for stronger weapons comes in later in the game rather than having all players reach Expert relatively early in the game. This has the oddity of incentivizing orcish weapons over regular, elven or dwarvish though.
• Make the enchantment of your weapon irrelevant to training or even make training slower with a positively enchanted weapon; if the weapon has magical homing assist technology, you’re not really building skill in how to use it that much.

Allow the player to complete the Invocation as long as they have ‘‘ever had 7 different candles in the game’’, even if they don’t have any right now. Flavoring this as the candle stubs being kept around and sputtering to life for long enough to do the invocation, immediately snuffing them afterward.

A bunch of scattered ideas for handling candles, given that the hero almost always wants to have only one lit at a time:

• Track all candles separately unless they have the exact same number of turns remaining.
• Merge all candles automatically, but still keep track of each one’s lifetime. (This would enable lighting multiple candles and then having one of the stack burn out.) When you light part but not all of a stack, the game internally picks the shortest candles.
• When candles merge, their lifetimes are averaged together.
• You can’t light more than one candle at once at all. (Not a great idea since it would destroy the mechanic of lighting a large amount of candles for more light).
• When candles merge, the candle with the shortest life automatically sacrifices as much of its lifetime as needed to “top up” the rest of the stack. That is, if the lifetime is 400, a candle with 50 turns remaining will merge with a candle with 375 turns remaining, making a stack of 2 candles with 25 turns remaining; when those 25 turns are up, it becomes a stack of 1 candle with 400 turns remaining.

Have the tab key be a shortcut for auto-attacking monsters (at range or at polearm range).