Adaptation

This spell can be cast in two different ways. The first, appropriate for battlefield use, has a range of 180 yards, a casting time of one turn, and duration of 1d4 + 2 turns. During this period, the affected unit can fight in one specific type of terrain (specified by the caster) as if it were the favored terrain (per BATTLESYSTEM rules) for that unit. While this spell is in effect, the unit gains no benefit when fighting in their actual favored terrain; the magically-enforced favored terrain takes precedence. The priest can cancel the spell before the duration expires if desired.
The second effect requires preparation in advance. The priest and unit must be within 100 yards of a place of worship dedicated to the casting priest's deity. The casting time is 5 turns.
At the conclusion of the casting, the unit gains the benefit described above, with two main differences. First, the unit does not lose the benefit of fighting in its own actual favored terrain (the unit effectively has two favored terrains). Second, the spell endures until the next sunset. Only priests of 12th level and higher can cast this variation.

[Tome of Magic]

Sphere: War
(Enchantment/Charm, Alteration)
Level: 3

Range: Special
Components: V, S, M
Duration: Special
Casting Time: Special
Area of Effect: One unit of up to 200 individuals
Saving Throw: None

Material Components:
Option 1: a pinch of clay dust
Option 2: the priest's holy symbol