Essence of the Immortals was for some time on the PTR for Patch 2.4 a drop from 25-person raid bosses in the Sunwell Plateau. Also, end-game bosses such as Lady Vashj, Prince Kael'thas, Archimonde and Illidan were dropping one essence per kill. Blizzard replaced the Immortals-system by having the three gates open automatically over time at equal intervals on all servers.