Quicklings are nymph-like monster introduced in SLASH'EM. True to their name they are extremely fast, having a speed of 30, exceeded by nothing except the air elemental. They are also able to attack with weapons, although not for very much damage. They only appear in Gehennom and the Lawful Quest.
It can be something of a dizzying experience to fight a quickling, as they may move as many as 3 times before you can even get one hit in. They do not have many hit points and only have one seduction attack, as opposed to nymphs' two. Thus they are not a huge threat, although they can be annoying when they flee after stealing an item, as even if you find them they can still be very difficult to catch, even with a ranged weapon. They are best attacked when they are approaching you to attack again, preferably with a good volley of projectiles.
As a polymorph form
The intrinsic speed and relatively low level of a quickling makes them an attractive polymorph form for a starting doppelganger. They are able to carry 1000 units of weight, and unlike air elementals, can see. A doppelganger will be able to infallibly polymorph into one upon reaching experience level 3, as opposed to 8 for an air elemental. Unfortunately, they do have very few hitpoints, and are too small to wield weapons, wear armor, or use doors. Still, they are useful forms for escaping or travelling through the Mines.