It's confusing because they are 2 different events. How the event works is there are 4 warder dragons in the raid dungeon (sleepers tomb) if you kill all 4 it awakens "the sleeper" a giant crystal dragon. There is then a event where this dragon goes on a rampage and kills everything then despawns. Its designed not to be player killable, and this event only happens once per server, once the sleeper has been awakened it never comes back. This is what the guild has done recently, 2022 on the p1999 green server, they didnt kill the sleeper just awakened it. In the rallos zek server event, they killed all 4 warders, and then killed the "unkillable" sleeper dragon, a much harder thing to do, and i believe it hasnt been repeated.