As I already said, nomads are good because of their speed! But what are the advantages of mummies? I don't like undead at all!

Mummies are good because they aren't too fast and like to chase after fairies or something else while they are being shot at. :D Nomads are sometimes good because of their dual-unit composition. :D Sometimes, 5 stacks stand on the battlefield and watch as only 2 stacks try to break through to the archers, which can be protected (using the terrain) by just two or three stacks. From this point of view, elves, griffins, and cerberuses are really bad. :D