City Under Siege.

Sunny is a naïve circus performer who dreams of inheriting his father's knife-throwing skills. However, his hostile colleagues continue to bully him, relegating him to a lowly clown. On a tour to Malaysia, Cheung and other performers discover a cave occupied by the Japanese army during World War II. Instead of finding treasure, the performers - including Sunny - are sprayed with a mysterious chemical that turns them into superhuman mutants...