"Mega Man X6" has an increased emphasis on rescuing Reploids over previous titles in the series. Whereas previous games rewarded the player with health or an extra life, "Mega Man X6" rewards the player with additional parts or other permanent prizes. Rescuing Reploids was made more difficult in this game with the addition of the Nightmare, which makes any Reploid it infects evil, thus rendering the Reploid impossible to save. The parts system was altered as well. Rather than attach a certain part to a certain armor, parts are attached to the character itself. The number of parts that can be equipped at once is dependent on the player's rank, which is increased by harvesting Nightmare Souls.