Nature elemental

A nature elemental was a creature summoned by a special priest spell for a single purpose: to return an area of land or water to its natural state, i.e., before it was touched by any form of humanoid civilization. When summoned, they began converting the area designated by the caster and continued for 24 hours or until a circular area of radius one mile (1.6 kilometers) had been cleansed, whichever came first.

Fundamentally, a nature elemental was composed of Air, Earth, Fire, Water, and spirit or life. If the caster was of sufficient level, then the spirit portion came from his or her deity, otherwise, the caster's spirit was used in the summoning and departed the Prime Material Plane with the nature elemental when the spell concluded, leaving the caster's lifeless body behind.

This summoned creature did not have free will, nor was it controllable. It performed the job for which it was conjured, relentlessly and without emotion, destroying all vestiges of civilization, including humanoid life, in its path and then dissipated. If any beings were foolish enough to attack it, it would defend itself and return the attack, but could not be lured away from its designated task.

Description
A nature elemental took the form of a massive, rough humanoid at least 35 ft (11 m) tall. Its body was made up of the biome in which it was summoned. For a typical temperate landscape, it would be composed of stone and dirt with grasses, shrubs, and small trees growing out of it, and miniature streams of water and small creatures running over its surface.

Combat
Regular combat with a nature elemental was an exercise in futility. Armies and weapons were just grist for grinding into raw materials that were immediately turned into soil, minerals, plants, and animals. Magic weapons and items had a chance to survive touching a nature elemental, but it was the same chance as resisting a disintegrate spell. The creature had the strength of a titan and could use its two massive fists to destroy structures or crush armed opposition.

While it remained in contact with its environment (including air), a nature elemental regenerated all damage every minute. The only way to kill it was to take all its prodigious health away in one tremendous blow, or somehow remove it from its environment so it could not regenerate.

Nature elementals were immune to protection from evil and similar spells intended to repel extraplanar creatures. By far the easiest way to get rid of a nature elemental was to cast the reverse of the spell that summoned it, dismiss nature elemental.

Habitat
Most sages speculated that these creatures did not have a single plane of origin, but were rather a very minor and limited avatar of the deity worshiped by the summoner.

Ecology
The nature elemental removed all traces of cultivation, deforestation, and civilization by breaking it down and reforming the area into its natural state. Plants grew to maturity within minutes after a nature elemental passed by. Air and water were purified, and animals were either deposited or attracted to the newly renovated area within hours. These creatures left behind a fully viable ecosystem in their wake.

History
The origin of the spell to summon a nature elemental has been traced back to the height of the first Netherese empire. References to it were found in ancient Netherese libraries and tombs.