The Ultras and monsters usually fight in a huge coliseum. However, after many monster battles, it turns out that Mephilas was innocent, and that the true cause lies in the meteor Tsuiphon, as well as a boosted Warrior Tsuiphon (taking the form of Dorako).
Ultraman then partners with Mephilas and with his "Ultra Crown" (a device that allows Ultraman to transform into Super Fighter without the cost of his own life energy,) and fights against Warrior Tsuiphon.