Aberration

Aberrations were creatures that were unnatural and had no place in the natural order of the Material plane or, in fact, most of the other known planes.

Description
These creatures did not fit into the natural world. Though some believed aberrations originated from the Far Realm, this was not true for all aberrations. Driders, for example, were unnatural crosses between drow and spiders. Created by the twisted goddess Lolth, the drow had their bodies aberrantly transformed, and thus were classed as aberrations.

Around the tumultuous time between the Spellplague and the Second Sundering, it was thought that aberrations were from, or touched, by the Far Realm. This made these creatures seem utterly alien to the Prime Material Plane, the fundamental planes, the parallel planes, or any other regions of the local cosmology.

Abilities
Aberrations generally all had bizarre anatomies, strange abilities, alien mindsets, or any combination thereof. Most aberrations had some form of darkvision, but as a group, they had no other special abilities or immunities.

Origins
Aberrations had no single point of origin, and many species had no real kinship or other relation to other aberrant species. Instead, aberrations came from strange, distant places and times.

Some aberrations came from extremely distant places on the Material plane, like the neogi and tsochari. Others were said to come not from distant locations, but from distant times; either as remnants of some antediluvian time or even preceeding creation (such as the aboleths), or as being from the future, as the illithids were said to be. Some aberrations were conjectured to be from an otherwhen world, a world with an alternate history where some event perverted the world from the natural course; such otherwhen worlds were not entirely real and as they grew more distant from the point of divergence, otherwhen worlds would begin to fade into nothingness.

Other aberrations came from planes that lay well beyond the known planes, most famously the Far Realm, where infinite different aberrations were said to dwell, and some known types such as cloakers and psurlons were said to hail from. The Ethereal plane, however, was strange enough that some aberrations (such as ethereal filchers, ethergaunts, and nilshai) were believed to have their origin there. Yet other strange planes included alternate Material planes that lay beyond the Plane of Shadow; such a plane was said to be the origin point of the grell.

Some aberrations did not come from any distant location or time, but were unnatural creations of dark, alien deities (like beholders and destrachan) or powerful but only questionably moral spellcasters (such as the chuuls and umber hulks).

Characteristics
The overarching characteristic that all aberrations shared was that they did not fit into the natural order of things. They had no natural predators, and no natural creature had the instincts to avoid them. Worse, aberrant powers warped and corrupted the area where they dwelled.

For people, just learning about aberrations was touched with peril, whether it be as "simple" as studying an aberrant language or more esoteric like spells one group devised. This was because in order to understand something of aberrations, one had to concepts and symbologies that were vastly different from humanoid ones, and such ways of thinking became harder and harder to set aside as one studied more, until sanity eventually slipped away.