"Everything" is a little broad still, and we're going to sidestep that while assuming that you aren't interested in having Rorschach thread out the mechanics of verifying prescription signatures or something. (If that does interest you, we can say more about that if you want?)
Following the organ trail will mostly lead to the cafeteria. Some are used in the lab for experimentation, but generally human parts are being harvested to feed back to patients later. All those killer mermaids love a good messy small intestine - it's practically spaghetti for monsters.

Mammon isn't in hiding, so it won't be difficult to find him! Was there a particular npc interaction you'd like for him to have?