Godzilla and Zilla Against Ultra-Ebirah is a kaiju film starring Godzilla, Zilla, and an Ebirah clone gone wrong named Ultra-Ebirah. Originally, the monster was supposed to be a clone of Hedorah rather than Ebirah.
A group of scientists are working on a new kaiju to stop Zilla, who is attacking New York once again. One scientist decides to use the DNA of a pre-existing kaiju. They use Ebirah's DNA to make a "super kaiju" with powers beyond belief. The project goes wrong, and "Ultra-Ebirah" destroys the laboratory and rampages through the city and makes it's way to New York, where it runs into Zilla. After a long fight, Zilla is thrown into the sky and lands in the ocean, where he presumably drowns. Ultra-Ebirah leaves the city and makes it to Monster Island, where it takes a rest. A week later, Ultra-Ebirah awakens and leaves for New York, not knowing that he is being followed by a swarm of Meganulon. Ultra-Ebirah makes it to Paris, where it starts destroying buildings again. Suddenly, the Meganulon swarm comes and attacks Ultra-Ebirah. The swarm gets the upper hand, when suddenly, Zilla comes out of the water for a rematch against Ultra-Ebirah. Ultra-Ebirah and Zilla's attacks prove worthless against the swarm. The two monsters are driven out of the city, outnumbered and outmatched by the bugs. The two monsters meet again swimming in the ocean, where they have another battle. Their battle awakens Godzilla, who is frozen in an iceberg at the bottom of the ocean. Godzilla breaks out and attacks the two, only to dicover that a much larger threat, the swarm, is spreading quickly through the world. Godzilla swims to the Earth to do battle with the swarm, followed by Zilla. Ultra-Ebirah takes the oppurtunity to go to some other city and continue his reign of terror. In Moscow, Godzilla and Zilla team up to take on the swarm. After defeating the swarm, they move on to the next city, where even more are waiting for them. Godzilla and Zilla defeat the swarm, then leave to fight the next. In Paris, Godzilla and Zilla emerge from the water and do battle with the next swarm. Suddenly, Megaguirus, the queen of the Meganulon. Godzilla and Zilla have a short fight with Megaguirus, before she flies away. The two monsters follow her to Washington, D.C., where they see Ultra-Ebirah attacking the White House. Suddenly, Megaguirus flies up and teams up with Ultra-Ebirah to take on Godzilla and Zilla. The four monsters have a huge battle, which ends with Megaguirus getting killed and Ultra-Ebirah escaping. After the fight, Godzilla walks off into the water, leaving behind Zilla. Zilla is suddenly captured by the government, and brought to a research facility. The government is doing tests on Zilla, when Ultra-Ebirah comes crashing into the building. Ultra-Ebirah kills some government scientists before being attacked by Zilla. Zilla and Ultra-Ebirah's fight ends up underwater. Godzilla swims up to help Zilla in battle. The two both manage to defeat Ultra-Ebirah, and swim away to Monster Island as government battleships and submarines approach. On Monster Island, Godzilla takes a rest as Zilla wanders off. The film ends at the bottom of the ocean as Ultra-Ebirah's "corpse" gets up and swims off.