Icho then returns to Il-Woo's house to tell him what happened at the refinery. Il-Woo then reveals this discovery to the authorities and urges them to not use the guided missiles because they will give him more energy, but his claims are brushed off and they proceed with the missile plan regardless. Il-Woo then goes to work on a chemical to defeat Yongary using a precipitate of ammonia. Yongary is then struck with Il-Woo's ammonia and missiles, which is enough to put him temporarily to sleep; however, Il-Woo believes the ammonia needs more work. Icho takes a light device from Il-Woo's lab and shines it on an immobile Yongary, which triggers him to wake up. To Icho's amusement, Yongary then begins dancing, but then returns to his rampage. Il-Woo loads the finalized ammonia onto a helicopter and dumps it on Yongary in the Han River, where Yongary collapses and dies. The following morning, Il-Woo is commended for his role in defeating Yongary; however, he cites Icho as the real hero for providing him with the information of Yongary's eating habits. In the end, Icho opines that Yongary was not evil by nature, but rather simply looking for food.
The screenwriter originally intended for Yongary to be a single-celled organism from space that mutated into a giant monster after exposure from radiation. Film critic and scholar Kim Song-ho revealed that in the original Korean script the name of the country conducting nuclear tests (the Middle East in the English version) was originally called "Orebia", with the location of the test being the "Goma Desert". In another part of the script, the "Goma Desert" was spelled as the Gobi Desert. Song-ho attributed this as likely a typo and that the writer intended to have Yongary originate from the Middle East.
Principal photography began on April 3, 1967, while the special effects photography commenced on April 6 with Cho Kyoung-min performing in the Yongary suit, who was paid ₩100,000 ($400 in USD). The special effects took three months to shoot and were filmed in two studios in Seoul. The miniatures and models cost ₩5 million ($20,000 in USD), the 12 constructed sets cost ₩7 million ($27,000 in USD), the Yongary suit cost ₩1.2 million ($5,000 in USD), and ₩500,000 ($2,000 in USD) was spent on gunpowder for pyrotechnics.
Keukdong (Far East) Entertainment Company employed staff from Equis Productions and Toei's special effects staff to helm the film's special effects. Masao Yagi, who built the Gamera suit for Daiei, supervised the construction of the Yongary suit. The character was designed in Korea, while the suit was built in Japan based on the Korean design. Director Kim Ki-duk found that the suit lacked terror and was disappointed with the final results, but proceeded to film with the suit since there was no time or money to produce a new suit. An optical printer was used for a few composite shots. Akira Suzuki designed the mechanical miniature props.
Lee Byoung-woo, the film's associate producer, acted as an intermediate between the South Korean filmmakers and the Japanese staff and helped train the South Korean staff in the special effects techniques used by the Japanese crew. Byoung-woo arranged for the Japanese crew to come work on the effects and is credited as the film's special effects cinematographer in the film's original Korean credits. The final film had 280 special effects cuts, with the crew filming three to five cuts per day. 15,000 lightbulbs were used for the miniature sets, with two-thirds of the available lighting equipment from studios in the country assembled for the film.
For its release in North America, Keukdong Entertainment Company sold the film to American International Pictures and released it under the new title Yongary, Monster from the Deep through their television division in 1969. AIP attached Salvatore Billitteri to supervise the English version's post-production and had the film dubbed by Titra Studios. Infamously, when the film was being sold overseas, the Korean producers (due to a lack of experience) shipped all of the original negatives and sound elements to Toei, who acted as the film's international sales agent. As a result, the original South Korean version of the film has been deemed lost and the AIP English dubbed version is the only version of the film that survives. The film was shown regularly during the '70s on syndicated television. U.S. ownership of the film kept changing: AIP was picked up by Filmways, Inc. in 1979, which merged with Orion Pictures, which was later acquired by Metro-Goldwyn-Mayer in 1997.
Historian Steve Ryfle noted that reviews at the time were "quite good". A reviewer for the Kyunghyang Shinmun praised the film's production values and perceived it as a savior of the Korean film industry, stating, "The miniature sets of the city of Seoul, or tanks, or fighter planes were delicate and real." The writer also felt that the film would "breathe fresh air into Korean cinema". StompTokyo.com felt the film was too similar to Gamera, the Giant Monster but stated that "Yongary is one of the better Godzilla-inspired rip-offs. The suit has some impressive detailing, like the four tail spikes, and the suit looks more impressive than those that would show up in the majority of the Gamera films. While the effects are rarely very realistic, there are a lot of them, with probably more city destruction than would show up in any of the original Godzilla movies made after this point."
Due to the original prints having been lost, the film became unavailable on television and home media in its native country for 44 years until it was broadcast on television in South Korea for the first time on June 19, 2011; however, it was the English version that aired with Korean subtitles taken from the film's original Korean script.
Film scholar and critic Kim So-Young published an essay in 2000 where he noted how the evacuation and destruction scenes in the original Godzilla film reminded Japanese audiences of the atomic bombings of Hiroshima and Nagasaki, the evacuation and destruction scenes in Yongary similarly reminded Korean audiences of the Korean War. Kim also addressed the film's theme of masculinity, stating that the astronaut and the young scientist are "tested to prove their masculinity throughout the story" and alludes to the country's crisis of masculinity at that time. Kim addressed that Icho is the real hero of the film, believing Icho to be a mirror image of Yongary and a symbol of Korea's future.
Ryfle & Song-ho 2016, 00:27:28. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 01:00:58. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 01:14:10. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:38:30. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:16:16. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:16:40. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 01:06:49. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 00:33:05. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 01:05:05. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 01:06:21. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 01:07:05. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 01:08:06. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 01:08:14. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 01:14:34. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:10:06. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 01:13:25. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 00:21:15. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:21:23. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 00:17:20. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:17:26. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:17:33. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
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Ryfle & Song-ho 2016, 00:24:52. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:41:10. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:26:05. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:26:32. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD
Ryfle & Song-ho 2016, 00:26:54. - Ryfle, Steve; Song-ho, Kim (2016). Yongary, Monster from the Deep Audio Commentary (Blu-ray/DVD). Kino Lorber. https://www.youtube.com/watch?v=RYkha2ehZHI&ab_channel=GORIZARD