The scenes involving Jet Li fighting himself were shot using Li and a stuntman with a build similar to his. The stuntman's face was painted green so that it could be digitally replaced with Li's face later.
Jet Li uses two distinct kung fu styles when portraying Gabe and Yulaw. The evil Yulaw uses Xingyi Quan, or "Mind-Form Fist" (loosely translated). As can be seen when he is training, it is a very linear, offensive style. Gabe on the other hand practices Bagua Zhang, or the "Eight Trigrams Palm". It is characterized by open palm fighting, with circular footwork. Both styles are two of the three main "internal" styles of Chinese kung fu - the third being Taiji Quan (Tai Chi).
The 'University Medical Center' where Gabe goes for the MRI is the North Hollywood Medical Center where the popular sitcom Scrubs (2001) is filmed.
The scene in which Yulaw is practicing his Xingyi while shackled and jailed is a reference to the famous Xingyi master Kuo Yun Shen who did the same thing when he was jailed.
During the shootout at the beginning of the film, the LAPD officers in the Anubis Universe are all armed with M4A1 carbine assault rifles fitted with the M26 Modular Accessory Shotgun System. At the time of filming, the M26 was an experimental shotgun being developed for the United States Army by C-More Systems, and it was not available to the public. The M26s used in the film were prototype versions loaned to the production by C-More Systems, under a promotional agreement; they were later returned to the company after filming was completed.