Transmutation
Level: Druid 2, Mystic Ranger 3, Ranger 3
Components: V, S
Casting Time: 1 standard action
Range: Touch
Target: One willing animal of Small, Medium, Large or Huge size
Duration: 1 hour/level (D)
Saving Throw: None
Spell Resistance: No
This spell functions like reduce person, except that it affects a single willing animal (not one with which you are engaged in combat, for instance). This decrease in size allows the animal to fit better into tight spaces, such as the typical dungeon room or subterranean passage. Reduce the damage dealt by the animal’s natural attacks as appropriate for its new size.
Source: Player’s Handbook (Page 269)