SRD:Cloak of the Manta Ray
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Cloak of the Manta Ray: This cloak appears to be made of leather until the wearer enters salt water. At that time the cloak of the manta ray adheres to the individual, and he appears nearly identical to a manta ray (as the polymorph spell, except that it allows only manta ray form). He gains a +3 natural armor bonus, the ability to breathe underwater, and a swim speed of 60 feet, like a real manta ray.
Although the cloak does not enable the wearer to bite opponents as a manta ray does, it does have a tail spine that can be used to strike at opponents behind the wearer, dealing 1d6 points of damage. This attack can be used in addition to any other attack the character has, using his highest melee attack bonus. The wearer can release his arms from the cloak without sacrificing underwater movement if so desired.