Mosswine are dirty pigs who love to roll around in dirth and have plants and fungus growing on them. Ew. Mosswine love to go to mushroom patches to eat/roll around/be pigs. As a result, killing and carving them will give you mushrooms of all sorts. They're just huge mushroom fans, don't judge! Mosswine are not inclined to attack you, the hunter, even if you go and attack them. They'll probably just roll over and die, and their companions will either be too focused on mushrooms to care, or will flee.