Deferred features

The NetHack source contains code for several currently unimplemented features. Some of them are marked deferred, so they may or may not make it into the next version.

Monsters
The beholder : a type of floating eye (in fact many eyes on stalks coming out of an even bigger eye; derived from Dungeons & Dragons) with 5 gaze attacks: slowing, sleep, disintegration, stoning, and cancellation.

Depending on how the gaze attacks work (none of them are coded yet), the beholder would be an exceptionally nasty enemy.

The shimmering dragon : This would leave shimmering dragon scales and let you create shimmering dragon scale mail, which would confer displacement. Monster displacement is not yet implemented, which may be why this dragon is not yet present. There would be corresponding baby shimmering dragons.

The vorpal jabberwock : A tougher type of jabberwock (level 20 vs level 15).

The vampire mage : The next step up from a vampire lord, with spellcasting abilities.

Burying
There is code for "burying" both you and monsters ("The floor opens up and swallows !"). You can be buried, and stay alive for a while (eventually suffocating), and you have the opportunity to tunnel out.

Other features
There is code that gives a 1 in 25 chance of applied bullwhips yanking a monster's weapon away from it, and it hitting you.

There is code that lets monsters use scrolls of fire as a last-resort offense.

There is code for creating force fields over an area of the map.

There is a hint that randomising the order of the elemental planes is a possibility.

There is code to give elves a luck penalty for wielding cold iron.

Obsolete features
Several monsters relating to the old Elf quest are still in the code: Earendil, Elwing, the Goblin King, and high-elves.