Ninja is an Arrow Dynamics/Vekoma steel roller coaster located in the Studio Backlot section of Six Flags St. Louis in Eureka, Missouri. The ride features a loop, a sidewinder, and a double corkscrew. It was originally built for and located at Expo '86 in Vancouver, B.C., operating as Scream Machine from May to October 1986. It began operating as Ninja at Six Flags St. Louis in 1989. The coaster was started by Arrow Dynamics, but when Arrow fell into bankruptcy, it was sold to Vekoma, who finished it. The ride is formerly shared a name with Blue Hawk at Six Flags Over Georgia until that coaster's retheming in 2016. Another roller coaster with the same name exists at Six Flags Magic Mountain, but that ride is an Arrow Dynamics suspended swinging coaster. The Ninja, like most modern roller coasters, requires a minimum of two employees to dispatch the train. One operates the main panel, which controls the restraints, gates, and has a section for the mechanics. The other operator stands at the remote enable. Both operators have to do an all clear sweep and thumbs up, then press their buttons at the same time.