Warhammer40k wiki on the wikia network has an article on Chaos Spawn where it's claimed that Nurgle eventually elevated Foulspawn to daemonhood (reportedly the only spawn to ever achieve this), but given its tendency to operate quite liberally with the source material, and the complete lack of inline citations, I'm quite skeptic of it. Regardless, he appears to be something vaguely toad-like with multiple appendages, a sickening aura and a liking for eating people. I'm not sure much more was ever published on the character.
