The Longbow of Diana should still provide reflection when it is in the offhand slot and not actively wielded.

Wielded, lit lightsabers should confer reflection, either partial or full, at a certain skill level. Not helpful against missiles or beams, but useful against rays.

Pets that know they have reflection (from an amulet, spell, etc) will freely attack floating eyes.

If you cast the spell of reflection while already having reflection from the spell but after you’ve gotten a message indicating it’s running out, you get the full duration of the spell rather than the reduced one.

Having both intrinsic and extrinsic reflection at the same time should make you fully reflect things as you would in vanilla, until the intrinsic times out.

Conceptually separate breath weapons from rays, making them not trivially reflectable. Make it possible to suffer reduced effects from a breath weapon, with the size of a worn shield a factor in that reduction.

Possibly make dragon armor of the same type as a given breath weapon (e.g. red dragon armor versus fire breath) reflect that breath weapon, and only that one.

If silver dragon scale mail is your only reflection source, or more generally if your only reflection sources come from your shirt and/or body armor, wearing a mummy wrapping over this prevents Medusa from seeing her reflection (though you are still considered to have reflection in all other respects).

Randomize the set of “critical” extrinsics and the base items that provide them in each game. I.e. instead of every game having a cloak of magic resistance, ring of free action, and amulet of reflection, the game could have a ring of reflection, a cloak of free action and an amulet of magic resistance.

Some way to make riding effective in the endgame (mainly addressing the problem that no steed can wear an amulet of reflection and usually dies to too much HP damage from ray attacks). This could be an artifact saddle that either gives your steed reflection or makes monsters focus only on the rider, or simply have the player’s reflection extend to their steed similar to how magic resistance does.

Wielding a mirror conveys partial reflection: you will reflect things 40 or 50% of the time.

If you get hit by something reflectable, have no other source of reflection, and prayer timeout is 0, your god may rarely intervene (“But it reflects somehow!”). This could either increase timeout a smallish amount or not increase it. Does not break atheist conduct.

Alternatively, instead of “using” prayer timeout, automatically spend a couple points of divine protection. Because you would have had to break atheist to get that, the atheist problem doesn’t apply.

Divine lightning (a god smiting you, particularly Moloch when you attack his high priest) should ignore reflection; it’s a “wide-angle” blast of lightning. Maybe this should apply to the lightning monster spell too. The high priest of Moloch should also be shock resistant.

New artifact Mirror Brand. It is an artifact short sword that grants reflection when wielded and when it hits an opponent, takes the higher of its own base damage roll and the other weapon’s (then adds its own enchantment to the result).

It is based on dNetHack, though it’s more akin to a generic mirror blades than the actual Mirror Brand artifact in dNetHack.

New artifact The Mirror of Venus, a mirror that confers slotless reflection. If you are female, you can invoke it to charm monsters; otherwise, invoking it will only pacify monsters. Will only be gifted to a female character.

(Male counterpart artifact is the Spear of Mars, #2756).

The proper way to make late-game elemental damage matter is to give late-game enemies elemental attacks with large enough damage to matter, which don’t care about reflection.

Disintegration rays have a small (on the order of 5% or 10%) chance of destroying the player’s reflection source instead of reflecting. This terminates the ray, so the player can’t get hit twice by it.

You can polish metallic shields by rubbing a towel on them. While it is polished and erosion-free, it provides reflection; but once it gets hit with some form of erosion it loses its polish and can’t be polished unless the erosion is removed.

More variety in ranged unreflectable elemental attacks, as a sort-of-nerf to reflection (all ranged elemental attacks currently in the game are reflectable). For instance, have enemies shooting fire arrows at you.

Artifact chaotic amulet Amulet of Splendor: provides every single amulet effect, as well as unchanging-ignoring controlled polyself when invoked. Wearing it conveys life saving (this WILL disintegrate the amulet if triggered), magical breathing, unchanging, poison resistance, ESP, reflection, strangulation (doesn’t kill you due to magical breathing but maybe it makes it so you can’t eat food or something while wearing it, or it autocurses), restful sleep, and gender change for as long as you wear the amulet. Base type is a cheap plastic imitation of the Amulet of Yendor.

Dragonbane gives 100% reflection versus dragon breath.

Gauntlets and boots of reflection.