The "Sewer Creep" is the colloquial name of a figure in the local rumors spread among the common folk of New Hezrath, though few have actually seen him. He has many odd descriptions and is rumored to prowl the sewers beneath New Hezrath.
The "Sewer Creep", in reality, is an old Catfolk druid who wants to live a quiet secluded life in the sewers. He commands local flora and fauna to violently deter anyone who, accidentally or deliberately, interferes with his peace.
During Return to New Hezrath, the party captured a Sun-in-Shadow cultist who told us he was forced into it by the Sewer Creep. He led the party into the sewers where they were attacked by swarms of insects and various animals (including another cultist) controlled by parasitic/symbiotic fungi. After we dealt with them, the Sewer Creep showed himself and helped the captured cultist escape. The Sewer Creep denied any involvement with the Cult and instead tasked us with eliminating a few demons who had infested his sewer. We did so, and he rewarded us with magic-ingused fungi.
The party in Will of D, when searching for clues on the demon Derek, ventured into the sewers to speak with the Sewer Creep. They found no evidence of demonic activity here. The Sewer Creep showed up, got very angry and called upon various creatures to chase the party out.