The Mummified Bog Man is a minor character who only appears once, and that happens to be in the episode, Hermit Ren. For a second, Ren's hallucination caused him to see him as a rather skinnier version of Ren, which scares Ren away, and he runs into a pile of mush, which he recognizes it as Stimpy and then Mummified Bog Man says "What a pile of mush.", which is supposedly Ren's imagination, and he later makes imaginary friends, and those are Ren's Anger, Ren's Fear, and Ren's Ignorance. Later, Ren was so mad at his friends, that he destroys Mummified Bog Man until all he had left was a bone.
Mummified Bog Man simply appears to be a reference to the Bog Body. ( http://en.wikipedia.org/wiki/Bog_body http://s.ngm.com/2007/09/bog-bodies/img/bog_feature.jpg )
- Even though Ren has destroyed Mummified Bog Man, he is seen in the background good as new as Ren walks out of the cave, along with other characters.