Complex sentence: The Demon is a multi-looping roller coaster at Six Flags Great America in Gurnee, IL with an identical twin at Paramount's Great America in Santa Clara, CA that opened in 1976 as Turn of the Century and was remodeled to the Demon in 1980.
Split into simpler sentences: The Demon is a multi-looping roller coaster at Six Flags Great America in Gurnee, IL with an identical twin at Great America in Santa Clara, CA. Both coasters opened in 1976 as Turn of the Century and were remodeled to the Demon in 1980.