Horrific, hunchbacked, green-skinned humanoids with frog-like heads and giant toothy fish mouths. Ancient creations of the Aboleths, when they ruled the world. Made to be warrior-slaves to wage war upon the land. They were left behind when the Aboleths left. They do not age, and can live forever, but are incapable of reproducing. They are all male. They take out their rage by enacting horrors upon others.
In Chapter 46, the party found a crew of Skum squatting in Rony’s house. Knowledge checks revealed them to be Monstrous Humanoids with darkvision. Good swimmers with multiple natural weapons and the Multiattack feat. They all possess a fairly decent amount of cold resistance.
In Chapter 50 (Part 2), a platoon of Skum attacked the Sellen Starling, seemingly as part of what they called the Great Harvest.
First Reference: Chapter 39
Other Notable References: Chapter 46, Chapter 50 (Part 2)