I present to you one of my latest creatures: Greed. On the left side of the picture you see a healthy Greed, unable to absorb any more nutrients but storing them inside of its body anyway. As a consequence, it is a normal occurrence for Greed to have misshapen body, deformed by the amount of undigested food stored within. Some of the little green fellas might even be alive in there.
Whenever Greed receives any damage, some of the nutrients are absorbed immediately and used to heal the wound, giving it great regenerative ability as long as its belly has any food in it.
Other creatures often get confused about Greed and won't see it as an enemy but rather as a source of food: instead of attacking it they would rather rub against it in hope to get some of the nutrients inside. Ironically, that usually means they are chewed to pieces and added to the Greed's food storage. However, sometimes a small creature makes its way inside while remaining alive, occupying one of the two stomachs (pic on the right). That creature then has an opportunity to feed on whatever Greed can't absorb and grow within like a parasite. Because of above-mentioned confused reaction, parasite creature will not attack Greed even if it grows some combat parts. That relationship, however, doesn't need to be parasitical: as the inner creature grows through the Greed's body, its combat parts can stick outwards and later used against enemies, giving Greed additional protection.