Rats in the Walls (d20)

From publisher blurb:

Dire rats and wererats make good d20 Fantasy adversaries, both because of the strong reactions they provoke from people and because the evocative (and often disgusting) locations in which they are often found are interesting places to fight. From new options such as the deadly tail fighting feat, the crippling curse of gutgnaw or the supernatural powers of the Rattenkonig, Rats in the Walls offers all the tools you need to give rats and their kin a starring role in your campaign.