|Home world:||Yapool's dimension|
|First appearance:||Ultraman Ace Episode 45: "Big Pinch! Save Ace!" (1973)|
Subtitle: Gas Super-beast (ガス超獣 Gasu Chōjū?)
- Height: 78 m
- Weight: 27,000 t
- Origin: Yapool's Dimension, Space
Gasegon was a monster from space, possibly one of Yapool's choju. He was concealed inside a black cloud and descended on a space craft. TAC was now aware of the disappearance and intended to investigate for signs of trouble. A boy was looking at his new telescope until he saw a red light headed for one of the oil tanks. TAC detected the force and it was located in the industrial area. After they found the monster with a Geiger counter, their jets fired onto a particular tank. After a few shots, Gasegon came out! TAC did not want to cause a nuclear explosion so they had to improvise. TAC used freeze bombs on the choju and it seemed to work until Gasegon used his own heat to melt the ice. Hokuto was shot down by the choju and became Ultraman Ace to fight Gasegon. Gasegon proved to be a tough fighter, but Ace eventually sneaked from behind and carried him into space. There, TAC shot their new laser to blow up the choju without harming any civilians.
- Gasegon's roar is a modified roar of the Toho Monster, Rodan.
- Although not physically seen, Gasegon is one of the monsters that makes up Beryudora's body in Mega Monster Battle: Ultra Galaxy Legend The Movie.
Powers and Weapons
- Smoke Cloud: Gasegon uses a cloud of smoke to descend on planets.
- Radiation: Gasegon is highly radioactive and uses this ability to heat up when frozen.
- Flame: Gasegon can fire streams of fire from his mouth.
- Toxic Gas: Gasegon can fire a toxic gas from his mouth.
|Ultraman Ace Kaiju & Seijin|
|Verokron | Yapool | Chameleking | Vakishim | Garan | Aribunta | Giron Man | Brocken | Alien Metron.Jr | Doragory | Muruchi II | Gammas | Zaigon | Alien Antira | Unitang | Sabotendar | Barabas | Ace Killer | King Crab | Cattle God | Cowra | She-Devil | Hotarunga | Black Pigeon | Android Couple | King Kappa | Zemistlar | Aprasar | Aprasar Fairy | Space Mask | Black Satan | Giant Yapool | Mazaron Man | Yojo | Mazarius | Alien Orion | Sphinx | Alien Hipporito | Lunaticks | Undergroundmon | Gitagitanga | Red Jack | Baktari | Coakes | Bad Baalon | Kaiteigagan | Dreamgillas | Soundgillar | Machless | Snowgiran | Namahage | Alien Fire | Firemons | Alien Steal | Kaimanda | Shishigoran | Iceron | Woo II | Fubigirara | Onidevil | Gasegon | Daidarahoshi | Hanzagiran | Verokron II | Yapool Woman | Univerlages | Aquarius | Alien Revole | Signalion | Geegon | Alien Simon | Jumbo King|