In order to find out which event is on, a single raid member can strip and start the event. The rest of the raid should wait in the pit below. If Red Riding Hood is on, the raid member is safe, and the rest of the raid can move up, as the event will not start until someone talks to Grandmother. The other two events will engage straight away and the person on stage will die quickly.
Special Note - It is possible to stand on the barrels on the ledge above Barnes the Stage Manager and have one person start the event and run up to the ledge and also stand on the barrels. Doing so will prevent death from the event starting, though in the case of the Oz event, Roar may still hit/kill at least one person. This is effectively the same effect as the giant wheel in the boat room of Deadmines, creating an "evade" bug issue.
After the event, a door on the side of the stage opens which leads to the Curator via some trash mobs (among them the lucrative Ghostly Philanthropists).
Successfully completing the Opera also enables you to reach the side entrance, making wipe recovery much quicker. Prior to patch 3.2.0 the door opened automatically when the event was completed, enabling raids to skip several trash pulls by leaving and reentering.
Moroes must be killed for the Opera event to be accessible.
There are mods that are able to show what events will appear prior to engaging the event itself. Natur Enemycastbar is such a mod (available from http://ui.worldofwar.net) but there are no mods dedicated to this as of yet and natur Enemycastbar can be fairly unstable on whether it shows it or not.
Use: For the next 20 sec, your direct heals grant Fecundity to your target, increasing the healing received by the target by up to 30. Fecundity lasts 10 sec and stacks up to 5 times. Equip: Increases spell power by 39.