Body Horror Roleplaying Game (2013)

From the introduction:

The game details six different Physical Mutations which progress over the course of play which as an inconvenience but end as horrific bodily changes. Each player will have been infected with one at the start of play and at each stage will suffer the consequences of bodily changes in the forms of increased insanity, pain, monstrous behaviour and revulsion at what they are becoming.

The Game Master decides the level of gore and gruesomeness allowed in the game; above all it should be played with an air of tragedy as the player’s realisation of their impending fate to sinks in. The Game Master is free to create new mutations and speed up or slow down the rate at which the mutations occur and progress and whilst long term campaign play is unlikely, it should make for a fun and unusual game lasting a few sessions.