Greasing your weapon prevents monsters from disarming it with a bullwhip (though the attempt may cause the grease to wear off it, like usual).

When a mind flayer removes the grease from your helm, its round immediately ends because it has to clean off its tentacles before attacking again.

Greasing an item slightly increases its weight. If the grease wears off, it reverts to normal weight.

Grease trap, which showers you with grease when triggered, greasing your wielded weapon and giving you slippery fingers and several turns of fumbling. Occasionally, your armor may get randomly greased.

May drop a can of grease with 0-2 charges when untrapped.

If #3671 (greasy floor) is implemented, the grease trap may automatically replace itself with the greasy floor trap or terrain as part of its effect.

A greased bag of holding prevents corpses inside it from spoiling like an icebox will.

If you are not wearing gloves, greased rings slip off your fingers as if you had greasy fingers.

Greased items should be immune to getting stolen out of the inventory (except perhaps if it’s a greased armor piece and the stealer is a nymph that charmed you into taking it off).

You can rub a towel on a greased item to remove the grease from it, just like wiping your face.

Fire damage is amplified for any creature who has greased fingers or equipment.

Greasy floor, a new type of terrain (or perhaps a trap?) that applies grease to any boots you are wearing and almost always makes you slip. Slipping on greasy floor (which can also happen by walking barefoot or with already-greased boots on) causes you to drop random items, some of which may get greased.

The player can create greasy floor by smashing a potion of oil or applying (multiple?) charges from a can of grease to the floor.

Creatures that move onto a greasy floor patch may “slip and slide and struggle to stay upright”, losing their next turn 70% of the time. This also happens to a creature standing on a greasy floor patch that tries to do something involving footwork (combat, moving off the square, etc) 30% of the time. Or for a more simplified implementation, the trap doesn’t have to cause loss of turn when moved onto (though it might still produce a message), but has a 70% chance of making the creature lose its next turn regardless of the action (still need to keep your balance to take out a scroll to read or zap a wand, for instance).

If implemented as a trap, it cannot be untrapped (except probably by the standard method of digging a pit on it), but will eventually wear out after a slightly randomized number of times it affects something. (This prevents you from setting a single one in Ludios and then standing back to watch the whole army get greased and fall over themselves.)

You can remove a cursed ring by greasing it.

You can guarantee you won’t choke on a comestible by greasing it beforehand.

You can apply a scroll of fire to a greased item to ungrease it. This consumes the scroll.

If you are wearing a greased cloak, it should not count as one of your carried items for purposes of determining if you can squeeze through a diagonal choke point.

With greasy fingers, you are incapable of playing flutes or harps, which require fine finger control. Attempting to do so just gives a message “Your fingers slip on the strings/valves”.

Possibly, attempting to play any instrument with greasy fingers makes you fumble and drop it, since even things like horns and bugles which don’t require finesse still need to be held.

Stone-to-fleshing a greased stone object should retain the grease on the resulting meat object.

Giant players can apply grease to their bodies to squeeze through diagonal choke points.

If you have a silver non-reflection shield, a towel, and grease, you can turn it into a shield of reflection by polishing it.

A weapon slipping out of your hand due to greasy fingers overrides it being welded to your hand by being cursed. Thus, you can get greasy fingers intentionally to get rid of a cursed weapon.

Greased scrolls and spellbooks, if they catch on fire, burn up and deal additional damage.

Oilskin cloaks prevent you from getting entangled in webs. Greased cloaks do too, but the grease may wear off in the process.

You can apply a towel to remove grease from items if your face and hands are already clean when you apply it.

A greased object thrown across the floor will slide an extra 2d4 spaces.

Greased items that get exposed to fire become flaming for a certain number of turns afterwards (and then the grease is gone).

You can light a greased sword on fire. Attacks with it will deal fire damage for a few turns until it burns out.