Weirds are creatures from the various inner and outer planes (including the demi-, para-, and quasi-elemental planes as well as the elemental planes).
They are sometimes encountered on the Material Plane, often in the employ of a powerful spellcaster. Bribery is the usual means of gaining the services of a weird, though some spellcasters resort to even more deceitful practices or trickery to gain the services of these creatures. Spellcaster beware! Weirds are intelligent creatures and do not take kindly to deception (unless they are the ones engaging in such trickery).
All weirds, regardless of their makeup, are serpent-like creatures about 10 feet long, and being of an evil and malign nature. Weirds speak the common language of weirds and the language native to their home plane. Some speak more languages, and still some can speak Common.
Weird from the Tome of Horrors Complete, Copyright 2011, Necromancer Games, Inc., published and distributed by Frog God Games; Author Scott Greene.