Despite being a South Korean production, the film's principal cast consists of Western actors such as Harrison Young, Donna Phillipson, Richard B. Livingston, Briant Wells, Brad Sergi, Dan Cashman, and Bruce Cornwell.

An alternative cut was later released with an altered plot, new footage, and updated special effects on January 20, 2001 as Yonggary: 2001 Upgrade Edition, which was distributed in North America as Reptilian.

Hughes is separated and finds an alien corpse with a fossilized diamond while Campbell uncovers hieroglyphics leading to the location of a dinosaur skeleton.

Two years later, an alien mothership arrives near Earth's orbit and destroy two American satellites that get the attention of soldier Parker, who reports it to General Murdock of the United National Defense Agency (UNDA).

Hughes finds Holly and reveals to her about the legend of Yonggary, the alien fossil, additional hieroglyphics, and that he was held by the U.S. government as a "guest" for the last two years.

Murdock orders General Thomas to dispatch his experimental Project T Forces, led by Parker, to attack Yonggary.

Hughes and Holly decode the additional hieroglyphics and uncover that the aliens are controlling Yonggary through a diamond-shaped receptor on his forehead and that "another great light will be sent to do battle."

Cycor initially gets the upper hand, but Yonggary emerges victorious in the end, forcing the aliens to flee.

The generals manage to stop the bomber at the last minute and the following morning, the UNDA transports Yonggary to a deserted island, where he can live in peace.

In addition to receiving financial support from the Hyundai Capital Corp. and Korean Technology Finance Corp., the film received financial and technical support from the Korean government (and the government of Suwon) by allowing the filmmakers access to military bases, hardware, and locations such as the Historic War Museum in Seoul, a location where filming has never been permitted before.

Before entering production, the film was pre-sold at $2.72 million after signing nine contracts of copyrights with Germany, Poland, Thailand, Turkey, and others.