In a lot of folklore, iron wards away elves. This could be implemented in the game in several ways:

• Elves take extra damage when hit by iron. Not as much as silver, but still appreciable.
• Elven players take a small amount of damage when putting on or wielding iron gear, but get no further penalty. (dnethack hurts their regeneration rate while wearing iron, which is another option).
• Possibly some detrimental effect when wielding iron weapons as well, a to-hit or damage penalty, or negating bonuses from dexterity, strength, and skill, or something.
• This is balanced by elven racial equipment being better (not improved; it’s already better).

Grimtooth can be used to engrave a special name, similar to Elbereth, that scares only elves and hobbits.

Elves sing while attacking, which automatically draws the attention of any other elves and orcs on the level.

Elves sometimes carry lembas wafers, dwarves carry cram rations, and orcs carry tripe rations.

New artifact Elfrist, a chaotic orcish dagger which can be named. It has bonuses against elves, of course, but also a smallish flat damage bonus versus any monster, so it might actually be useful to name it early.

Orcish characters will never be able to tame elves, and elvish characters will never be able to tame orcs.

When polyselfed to foocubi of the appropriate gender, #monstering will seduce (i.e. de-robe) @ monsters.

Elves can engrave Elbereth and use it on the player, scaring them.