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Animal Reduction

(Masters of the Wild: A Guidebook to Barbarians, Druids, and Rangers)

Transmutation
Level: Druid 2, Ranger 3,
Components: V, S,
Casting Time: 1 action
Range: Touch
Target: One willing animal of size Small, Medium-size, Large, or Huge
Duration: 1 hour/level
Saving Throw: Will negates
Spell Resistance: Yes

You reduce the target animal's size by one category.
For example, a Large tiger affected by this spell becomes a Medium-size tiger.
This decrease in size allows the animal to fit better into tight spaces, such as the typical dungeon room or subterranean passage.
The size change also has a number of other effects, as given in the Monster Manual and summarized below.
If this spell would cause any ability score to drop to 0 or below, that score instead becomes 1 while all other effects apply normally.
Huge to Large: The subject loses 8 points of Strength, 4 points of Constitution, and 3 points of natural armor, while gaining 2 points of Dexterity, a +1 bonus to AC, and a +1 bonus on attack rolls.
Overall, this change results in a -3 penalty on melee attack rolls, a +2 bonus on ranged attack rolls, a -4 penalty on melee damage rolls, a -1 penalty to AC, and -2 hit points per Hit Die.
The subject's lace/reach becomes 5 feet by 10 feet/5 feet.
Large to Medium-Size: The subject loses 8 points of Strength, 4 points of Constitution, and 2 points of natural armor, while gaining 2 points of Dexterity, a +1 bonus to AC, and a +1 bonus on attack rolls.
Overall, this change results in a -3 penalty on melee attack rolls, a +2 bonus on ranged attack rolls, a -4 penalty on melee damage rolls, no change to AC, and -2 hit points per Hit Die.
The subject's reach becomes 5 feet by 5 feet/5 feet.
Medium-Size to Small: The subject loses 4 points of Strength and 2 points of Constitution, while gaining 2 points of Dexterity, a +1 bonus to AC, and a +1 bonus on attack rolls.
Overall, this change results in a -1 penalty on melee attack rolls, a +2 bonus on ranged attack rolls, a -2 penalty on melee damage rolls, a +2 bonus to AC, and -1 hit point per Hit Die.
The subject's face/reach becomes 5 feet by 5 feet/5 feet.
Small to Tiny: The subject loses 4 points of Strength while gaining 2 points of Dexterity, a +1 bonus to AC, and a +1 bonus on attack rolls.
Overall, this change results in a -1 penalty on melee attack rolls, a +2 bonus on ranged attack rolls, a -2 penalty on melee damage rolls, a +2 bonus to AC, and no change to hit points.
The subject's face/reach becomes 2 1/2 feet by 2 1/2 feet/0 feet.