[Black Dragon]

Well, it seems to me that Mudokons and Glukkons are omnivorous, meaning they eat basically anything that they can, like humans. Mudokons appear that way since, as you said, they were fed Paramite Pies, Scrab Cakes, and Meech Munchies, plus it is easy to imagine them gathering fruits and berries from the forests. If you notice the shape of a Glukk's front teeth, they could be used for both meat and plants. Sligs I'm not too sure of, but I can see them also as omnivores. I tried to use a Scientific approach, knowing me I probably messed up somewhere, but yeah, that's what I think.