To enter the illusion event you will require an Illusion Association that acts like an invitation to the event. In order to obtain this item you must combine a Pledge Of Blood and an Scroll of Blood(of the same level), along with one Jewel of Chaos at the Chaos Goblin in Noria:
A successful combination will result in the Illusion Association
Note: The combination can fail resulting in the loss of all materials.
Illusion temple lvls
Once the event start has been announced you have 5 minutes time to go to the Illusion Temple Guard (Lorencia 130,130) and register for the level range you are in using the appropriate Illusion Association: