The psionics system was again revised for the 3.5 edition of the game, in the "Expanded Psionics Handbook" (2004). This change streamlined the system by eliminating most power "chains", replacing them with the ability to augment powers by spending additional power points, as well as eliminating the psionic combat system that had previously been employed. A key change was changing powers that had previously been keyed to a different ability score for each disciple to a single ability score depending on character class. The book also introduced other races, such as the "Elan", psionic characters who had achieved immortality. The May 2004 issue of "Dragon" introduced the "Athasian elan" as a playable character race for the Dark Sun campaign setting.