"Humans are unfair creatures. I understand why only humans survived since ancient times"
- ―Shin Hayata
Mystery Comet Tsuifon (怪彗星ツイフォン Kai Susei Tsuifon) is the 25th episode of Ultraman. On the DVD release, it is only called The Dreaded Comet Tsuifon/The Dreaded Comet Twenty-Four.
When the giant comet Tsuifon was headed towards Earth, the SSSP division in Paris discovered that its cosmic rays might set off unprotected Hydrogen bombs. Japan's SSSP sent members Shin Hayata, Daisuke Arashi, and Mitsuhiro Ide to search for six missing hydrogen bombs in the Alps. Shortly after the men arrived in the Alps, Tsuifon had already passed over the Earth, but its presence disturbed the kaiju Guigass, then later Dorako. Still in search of the missing bombs the SSSP found another generation of Red King (generation II), who had the missing hydrogen bombs on his neck.
Red King then found the two previous kaiju locked in combat and decided to join. Both he and Guigass ganged up against Dorako and beat the kaiju mercilessly. Red King viciously tore Dorako's wings off, and Dorako died of its injuries soon afterward. Guigass was driven off by Red King and fell victim to the Extreme Drought Bomb deployed by the SSSP. All three monsters apparently precipitated out of a fragment of comet debris, or were awakened by the comet's radiation; it is not entirely clear, but the comet somehow triggered their appearance. Apparently Red King now presented an extra danger, as it had swallowed six long-lost hydrogen bombs. Ultraman appears and ultimately paralyzed Red King and raised it off the ground with the Ultra Air Catch. He then used two of his Ultra-Slashes to slice Red King into thirds. Ultraman took the head and neck portion and flew away into space with it to allow the H-bombs to detonate harmlessly.
- Toshio Muramatsu (ムラマツ・トシオ Muramatsu Toshio): Akiji Kobayashi (小林 昭二 Kobayashi Akiji)
- Shin Hayata (ハヤタ シン Hayata Shin): Susumu Kurobe (黒部 進 Kurobe Susumu)
- Akiko Fuji (フジ アキコ Fuji Akiko): Hiroko Sakurai (櫻井 浩子 Sakurai Hiroko)
- Daisuke Arashi (アラシ・ダイスケ Arashi Daisuke): Sandayū Dokumamushi (毒蝮 三太夫 Dokumamushi Sandayū)
- Mitsuhiro Ide (イデ・ミツヒロ Ide Mitsuhiro): Masanari Nihei (二平 政成 Nihei Masanari)
- Isamu Hoshino (ホシノ・イサム Hoshino Isamu): Akihide Tsuwaza (津沢 彰秀 Tsuzawa Akihide)
- Ultraman (ウルトラマン Urutoraman): Masao Nakasone (中曽根雅夫 Nakasone Masao) (grunts)
- Narrator (ナレーター Nareta): Koji Ishizaka (石坂浩二 Ishizaka Koji)
- Ultraman (ウルトラマン Urutoraman): Bin Furuya (古谷 敏 Toshi Furuya)
- Guigass (ギガス Gigasu): Minami Akirai (南明 Akira Minami)
- Dorako (ドラコ Dorako): Ikeda Fumio (池田文男 Fumio Ikeda)
- Red King (レッドキング Reddo Kingu): Suzuki Kunio (鈴木邦夫 Kunio Suzuki)
- Ultraman Volume 7 features episodes 25-28.
- Ultraman The Complete Series features all episodes.
- Originally, Gorgos (from Ultra Q) was intended to be the kaiju that fought Guigass and Dorako in this episode, but he was replaced by Red King II for unknown reasons.
- This episode was later featured in New Ultraman Retsuden episode 17 "The Dreaded Comet Tsuifon! The 3 Roaring Monsters!!."