Animal Growth {Wizard}

When this spell is cast, the wizard causes all designated animals, up to a maximum of eight, within a 20-foot-square area to grow to twice their normal size. The effects of this growth are doubled Hit Dice (with improvement in attack rolls) and doubled damage in combat. The spell lasts for one round for each level of experience of the wizard casting the spell. Only natural animals, including giant forms, can be affected by this spell.

Reverse: Shrink Animal

The reverse, shrink animal, reduces animal size by half and likewise reduces Hit Dice, attack damage, etc.

[Player's Handbook]

Reversible

School: Alteration
Level: 5
Rarity: Common

Range: 60 yards
Components: V, S, M
Duration: 1 round/level
Casting Time: 5
Area of Effect: Up to 8 animals in a 20' cube
Saving Throw: None

Material Components:
(both versions) a pinch of powdered bone (consumed)