Elementals are creatures composed of one of the four classical elements (air, earth, fire, or water). They have been part of the D&D game since its beginnings, and have appeared in every edition of the game.
Originary from the Elemental Planes, elementals are incarnations of the elements that compose existence, and are as wild and dangerous as the forces that birthed them.
Elementals come in all imaginable sizes and shapes, most of the times resembling sheer chaos as the enegies they embody. As they are not living creatures in the strict sense of the word, they don’t eat, sleep or subject to mind-affecting effects.
In some settings, elementals are often ruled by powerful, singular beings called archomentals. These entities fall into two groups, the Elemental Princes of Evil (Cryonax, Imix, Ogrémoch, Olhydra, Yan-C-Bin), and the Elemental Princes of Good (Ben-hadar, Chan, Sunnis, Zaaman Rul). In the Dark Sun setting, they are called ‘elemental powers’ and worshipped by some of the residents of the world of Athas. Athasian clerics forge pacts with one element or paraelement; and from that moment their spells are powered by the spirits of that element. An Athasian cleric who is gifted with well-developed psionic abilities can turn into an elemental being when he reaches the 20th level. This transformation is, at first, temporary; but as the character advances through the levels, it becomes permanent.
Paraelementals and Quasi-elementals
Paraelementals fuse two of the classic elements into a single dangerous creature: we know of the existence of ice (air and water), magma (earth and fire), ooze (earth and water), and smoke (air and fire) paraelementals. Quasi-elementals are a fusion of one of the classic elements and either positive or negative energy. When infused with positive energy, we know of lightning (air), mineral (earth), radiance (fire), and steam (water) quasi-elementals, and when derived from negative energy, we can find ash (fire), dust (earth), salt (water), and vacuum (air) quasi-elementals.
Elementals are bound so that their energies may be used to power the device to which they are connected. The art of binding elementals is a craft mastered so far only by the gnomes of Khorvaire. The best examples of this are elemental-powered airships and the Lightning Rail, but elementals can also be bound to weapons and armor as well.