Stassen founded nWave Pictures in 1994, producing CG ride films including Devil's Mine.
Starting in 1997, Stassen began focusing on large-format films, directing Thrill Ride: The Science of Fun and Alien Adventure.
In the late 1990s, Stassen directed a succession of 3-D large-format films, including Encounter in the Third Dimension and Haunted Castle.
[citation needed] Stassen's first feature-length animated film, Fly Me to the Moon, was released in North America on 15 August 2008 on both regular-size and IMAX screens, exclusively in 3-D.
Further animated features directed or co-directed by Stassen include A Turtle's Tale 2: Sammy's Escape from Paradise (2012), The House of Magic (2013), The Wild Life (2016) and The Son of Bigfoot (2017).