Tortoise Shell

(Spell Compendium, page 221, DnD 3.5)

Transmutation

Level: ; Druid 6
Components: V, S
Casting Time: 1 standard action
Range: Touch
Target: Living creature touched
Duration: 10 minutes/level
Saving Throw: None
Spell Resistance: Yes (harmless)

In the blink of an eye, the creature you touched grows the armor plating of a tortoise across its torso and a tough, leathery skin elsewhere.

Tortoise shell grants a +6 enhancement bonus to the subject's existing natural armor bonus. This enhancement bonus increases by 1 for every three caster levels beyond 11th, to a maximum of +9 at 20th level.

The enhancement bonus provided by tortoise shell stacks with the target's natural armor bonus, but not with other enhancement bonuses to natural armor. A creature without natural armor has an effective natural armor of +0, much as a character wearing only normal clothing has an armor bonus of +0.

Tortoise shell slows a creature's movement as if it were wearing heavy armor. An elf subject to tortoise shell, for example, would have a speed of 20 feet and could run only 60 feet per round. The spell affects only a creature's speed; tortoise shell doesn't carry an armor check penalty or an arcane spell failure chance.