Eating an amulet of reflection (which doesn’t provide any intrinsic) causes you to “reflect on your inner self”, providing enlightenment.

Artifact polearm of unspecified type The Ten-Foot Polearm. When wielded, it confers immunity to stoning from c corpses, artifact blasts, and special damage from bane artifacts that hate you, because “you don’t touch them with a ten-foot pole”.

It is possible to get a scroll of genocide both blessed and cursed at the same time. The effect of this is that it prompts for a single monster, genocides most of that monster, and sends in the remaining several monsters who are now looking for revenge.

Alternatively, make this a confused effect instead of opening the can of worms of allowing items to be simultaneously blessed and cursed.

A variant cursed effect of a scroll of genocide: it removes most monsters of a given species, but sends the survivors to you looking for revenge.

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

A simpler version of this idea would be simply to burn off a weapon’s grease when it’s exposed to a fiery monster.