Alien Mefilas

Alien Mefilas, sometimes spelled Alien Mephilas, are a race of intelligent aliens that have attempted to conquer the Earth several times.

Ultraman
Alien Mefilas attempted to conquer the Earth in order to show off his abilities to his fellow aliens who had tried to conquer it before

Alien Mefilas' planned to convince a child of the Earth to give him the Earth in exchange for a new star. Alien Mefilas targeted Akiko Fuji's younger brother, Satoru, for his plan. Mefilas communicated with Satoru and made the air show he was watching vanish before replacing it with a freighter vessel that he destroyed in midair. Mefilas then captured Satoru, alongside his older sister and Hayata.

Alien Mefilas turned Fuji into a giant and placed her in the middle of a city. He made several attempts to get Satoru to give him the Earth in return for a star, telling him he wanted to "challenge the heart of an earthling". Hayata laughed at Mefilas' failures to win over Satoru and attempted to reach for the Beta Capsule to transform into Ultraman but Alien Mephilas froze him before he could.

When Satoru stopped responding to him, Alien Mefilas made the giant Fuji go on a rampage in the city. The SSSP tried to keep the police from hurting Fuji. Alien Mefilas then revealed his presence to them and replaced Fuji with illusions of Alien Baltan, Kemur Man, and Alien Zarab. The SSSP soon located Mefilas space ship, and an air strike was sent.

The Science Patrol rescued Fuji and Satoru, and Hayata was able to transform into Ultraman to face off against Alien Mefilas, who had grown giant. Alien Mefilas shot down Ultraman's offer for him to leave and attacked him. The battle was very evenly matched, with both Mefilas' physical strength and attacks being on par with Ultraman's. However, Alien Mefilas soon surrendered, seeing no point in continuing the fight and prepared to leave. However, before his departure, Mefilas told to Ultraman that they would meet again and that he would get his revenge.

Ultraman Taro
A second alien Mefilas, named Alien Mefilas II came to Earth in episode 27 to conquer it. He initially attempted to kill off humanity with a bio-weapon called the Mandarin Gas, but when the weapon was destroyed by ZAT, Mefilas revealed himself and attacked ZAT directly. However, Kotaro transformed into Ultraman Taro to fight Mefilas. Mefilas proved to be no match for Taro, and was killed when Taro used the Storium Ray to reduce his body's composition to slime.

Ultraman Mebius
Alien Mefilas appears in episodes 42 to 47 of the series, and is revealed to be a member of the Four Heavenly Kings, a quartet of generals who served directly under Alien Empera.

Following Yapool, Deathrem and Glozam's defeats, Alien Mefilas came to Japan to mind control the populance and turn them against Ultraman Mebius. The original Ultraman arrived on Earth to stop Mefilas but couldn't fight him as he hadn't yet harmed anyone. However, Mirai exposes Mefilas' mind control to Team GUYS, and Ultraman and Ultraman Mebius both attack and double team Mefilas. Rather than continue fighting him, however, Ultraman instead persuades Mefilas to surrender. Mefilas accepts Ultraman's offer and promises to Ultraman that he will show up to fight him once again. Unfortunately, Mefilas was killed soon after by the Alien Empera.

Ghost Reverse
Alien Mefilas was later revived as a ghost alongside his fellow Heavenly Kings in the Monster Graveyard. Mefilas and the other Heavenly Kings planned to revive Alien Empera via his remains in Mechazam. However, they were all destroyed again by Ultraman Ace, Ultraman Taro, Ultraman Mebius and Ultraman Hikari.