What is a skulk?

[Deamoclese]

In the Dungeon Magazine adventure: Life's Bazaar (adventure path series, first adventure), it makes mention of a humanoid creature called a Skulk... it gives stats but gives me no idea what book it came from.... I can't describe the darn thing cus it didn't include that... was this monster published in a book somewhere??

 

[Knight Otu]

At the beginning of the adventure should be some text about the source - it's the Fiend Folio. Also, there are stats for the skulk in the Tome fo Horrors.