The series contains numerous power-ups, which are held in boxes that appear throughout levels. An icon indicates what it contains, and the player releases the item by destroying the box. Common items in boxes include rings, a shield, invincibility, high speed, and extra lives. "Sonic Colors" introduces the Wisps, a race of extraterrestrial creatures that act as power-ups. Each Wisp has its own special ability corresponding to its color; for instance, yellow Wisps allow players to drill underground and find otherwise inaccessible areas.