That is a really cool idea and it is most possible because of the fact we already visited Necrum Mines. I think Necrum mines was Under ground I am not sure. Anyway I can see all of the inhabitants to have glowing eyes like the Raison and the Glukkens and the Rats. Maybe there will be this lost colony of Mudokins living under ground but they don't look like normal Mud's. They have glowing eyes too and they look deformed. Kind of like the mole people. These Muds never saw the land above and they are evil too. I can see the whole Mudokin colony chasing Munch and Abe through caverns and then all of a sudden that machine creature appears and all the freaky Muds start fighting that. So now we don't only have the industrialist to worry about but the underground naturalists as well. Under ground deformed Mudokins. sweet!
