Grue

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A grue is an evil creature native to one of the elemental planes. They are prized by spellcasters because each houses a Spell object at its core, which contains a single spell suitable for copying to a spellbook.

Grues are considered pests on their own planes, one step above Elemental vermin, but not by much. They are created from evil spells cast in their respective planes.

The Chaggrin (earth grue) hails from Plane+of+Elemental+Earth.
The Harginn (fire grue) hails from the Plane+of+Elemental+Fire.
The Ildriss (air grue) hails from the Plane+of+Elemental+Air.
The vardigg (water grue) hails from the Plane+of+Elemental+Water.

Sources: 
Complete Arcane
Planescape Monstrous Compendium Appendix I
Secrets of the Lamp
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