When this spell is released, the caster causes up to eight animals within a 20-foot-square area to grow to twice their normal size. The effects of this growth are doubled Hit Dice (with resultant improvement in attack potential), doubled hit points (except hit points added to Hit Dice), and doubled damage in combat. Movement and AC are not affected. The spell lasts for two rounds for each level of the caster. The spell is particularly useful in conjunction with a charm person or mammal spell.
The reverse reduces animal size by one-half, and likewise reduces Hit Dice, hit points, attack damage, etc.
The material component for this spell and its reverse is the caster's holy symbol and a scrap of food.
Notes: Common for druids (PHB).