Ultraman Mebius
This alien reappeared in the series Ultraman Mebius.
In this series, Alien Mephilas has formed an alliance with Yapool, Deathrem, and Glozam to create "The Four Heavenly Kings." A Coalition of aliens that serve a higher up entity known simply as "The Emperor."
After Yapool, Deathrem, and Glozam were all defeated, Alien Mephilas comes to Japan in a new ship and this time he uses mind control on the populance to turn them all, as well as Team GUYS against Ultraman Mebius. He further panders to the people of Japan by demonstrating his power to destroy a Gromite he creates only to destroy shortly after out of false heroism and accolade. All the while, the original Ultraman returns to confront Mephilas into stopping him from doing any harm to the humans. However seeing as Mephilas has not harmed any humans, Ultraman cannot fight him. Eventually Ultraman Mebius (as Mirai) manages to show Team GUYS the control that Mephilas has put them under, Mephilas tries to attack them out of self-defense and shortly afterwards appears himself to battle Mebius. Ultraman shows up and both Ultraman and Ultraman Mebius shortly double-team Mephilas. After shrugging off one of Mephilas's lightning attacks, Ultraman persuades Mephilas to surrender in order to save his own life knowing that he cannot beat two Ultras and Team GUYS. Once again, Mephilas wisely surrenders and even acknowledges to Team GUYS of their efforts from defeating the other three Aliens. However before leaving, he promises to Ultraman that he would return to personally challenge him again. However, the promise was shortly broken as Mephilas was then killed himself by the entity of the Emperor himself: Alien Empera.
This Alien Mephilas is in fact the original Alien Mephilas that fought the original Ultraman. He shows signs of experience as he tries to occasionally warn the other aliens not to underestimate the humans or the Ultras as well as respect to those who have bested him in the past (namely Ultraman.)
Read more about this topic: Alien Mephilas