You can dip oil into booze or vice versa to create a new type of potion (“potion of firebomb” or “potion of molotov cocktail”) that is never randomly generated, which is primarily intended to be lit and thrown like oil, but results in a much more powerful fireball than oil alone would produce.

Effects when drinking this potion are unspecified. Since oil has minimal effect when you drink it, it likely just works like booze or diluted booze.

The game should not assume heroes all carry an unlimited invisible box of matches to light candles and lamps with. Doing that should require a fire source, whether that is Fire Brand, lava, a fire trap, the wand of fire, the fireball spell, or an already lit candle, lamp, or potion of oil. There could also be a new “lighter” tool which enables you to light things, but can get lost or run out of charges.

You can pour a potion of oil over yourself to temporarily block any invisibility for 200 turns. While oiled, you take double damage from any fire source, and you can slip through boulders diagonally without worrying about how much stuff you’re carrying.

Iron golems rust in multiple stages, like iron items, rather than all at once. Each stage cuts its maximum HP by 20 (so a rusty golem has 60 max HP, etc.) Applying a can of grease will remove the rust and restore its max HP to normal, and may prevent further water damage for a little while. The golem may also quaff a potion of oil, which has a similar effect, except it also restores current HP as well as maximum by the amount of erosion removed.

Iron golems that rust to death may rarely leave behind a statue (ideally made of iron material) which is implied to be its rusted husk.

Remove holy/unholy water’s ability to bless/curse items. Instead, make blessed and cursed oil serve the same functions. Dipping a stack of uncursed oil in holy/unholy oil will bless or curse the stack, as currently works, but since oil is significantly less easy to get than water, this makes mass-blessing of items harder to accomplish.

Anointing an item with holy or unholy oil ignores effects that would normally happen because of the oil. For instance, dipping an oil lamp in holy oil will just bless it, or do nothing if it was blessed already.

Priests now start with a stack of 4 holy oil.

Water doesn’t get outright removed - other things still dilute to it and turn into it in random alchemy - but it’s not much use anymore except for on-the-go dilution.

Not specified whether you could pray to get a stack of oil potions on an altar blessed, or whether this wouldn’t work.

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.)

If an (unlit) potion of oil breaks on your head, you get slippery fingers.

Dipping Frost Brand into water potions (or possibly any freezing-eligible potion, which is most of them) should freeze and shatter the potion. Likewise for Fire Brand, which should boil potions and ignite (but not explode) oil it’s dipped into.

When a thrown potion of oil lands on (or possibly even passes over) a furnace/forge, it ignites and explodes.

You can apply a can of grease or potion of oil to a door to guarantee that it will close and open without resisting.

Sconces (perhaps a \ found on the walls of dark rooms, and in dark Mines levels, that may contain (lit or unlit) candles. You can untrap or loot them to remove the candle. Could also generate with an oil lamp, which would give you a potion of oil or a partially filled oil lamp when looted.

When a potion of oil gets hit by fire, it ignites and explodes.

Potions of acid and oil are immune to freezing and shattering.

Dipping water into oil doesn’t count as random alchemy.

Fire bolts light potions of oil on the ground that the bolt is zapped over, and cold bolts snuff them.

Make potions of oil undilutable.

Potions of oil heal iron golems when quaffed.

Make potions of oil more common, so that the player has more area-of-effect combat options (for throwing firebomb potions of oil). Possibly allow hardware stores to stock them.