 Another goal was to encourage players to revisit completed levels; Sonic Team accomplished this by adding segments requiring certain types of Wisps to levels preceding their first appearances.The Wii version makes use of the PhysX physics engine, previously used with 2007's "Sonic and the Secret Rings", while the DS version uses the same engine used in the 2005 entry "Sonic Rush" and its sequel.According to producer Takashi Iizuka, "Sonic Colors" was designed to appeal to a casual audience, particularly children and fans of the "Super Mario" series.