For the love of the Emperor, how did we miss nasty, pus-filled, disease-carrying, bowel-voiding Nurgle?
Nurgle also makes an appearance in Warhammer. Also, Ogre and Beastman eating habits, and practically everything involving the Skaven, depending on your tolerance for rats; let's not get started on Clan Moulder's horrifying, painful and usually pointless "experiments" on living things.
Exalted: The Phylactery Womb. It's a little girl that stores Infernal exaltation spark inside her body... turning her into a bloated thing that oozes disgusting liquid from every orifice of her body. And this is one of the tamer description.
FATAL has a lot of game mechanics focusing on particular body parts. It can get rather disgusting and frightening rather quickly.
The Child-Thing in the standalone adventure "Mr. Corbitt". It's a huge walking tumor with too many baby-doll-like arms that constantly spews... something from an orifice on the top of it somewhere. It's heavily implied that this liquid is pus, blood, or some sort of bodily waste.
Hypatia Mathers by the time you find her in Masks of Nyarlathotep also qualifies. She's grotesquely pregnant with the Eldritch Abomination in question's spawn and has the bloated body-turned-womb-sack to show for it. The campaign book actually describes her like that. Oh, and of course the players get to eventually see her give birth to it by violently having her head explode.