This cloak is the result of an unsuccessful attempt to create a standard Cloak of the Bat. Fortunately, the error resulted in the creation of an unique magical item. Fashioned from the pelts of giant rats, the cloak is otherwise seemingly unexceptional. However, the cloak bestows upon the wearer the ability to polymorph into a giant rat. This form is maintainable for up to 1 hour at a time, but after a use of any duration, the cloak must recharge for a like period of time. The wearer gains the movement rate, attacks, and AC of a giant rat, but retains hit points, saving throws, THAC0, etc. of their normal form.

Once per day, the wearer may cast the 2nd level spell Summon Swarm; only rats answer the summons, and the spell operates at 10th level. While wearing the cloak, the owner is immune to nonmagical diseases. The cloak provides a +2 bonus to AC, which extends to the user even while in giant rat form.

Two additional magical items are usually associated with this cloak. The first is a Amulet of Non-Detection used as a clasp for the cloak, with the second being a Portable Hole sewn to the inside lining.