These are the "event entry’" rules, which will enable you to start the event:

-There isn’t a Dragon Power requirement. To join this event, you just have to be part of a Den. Keep in mind, however, that you have to have 750 Dragon Power to join a Den

-There isn’t an active player requirement in order for a Den to play in the event. So don't worry if some of your den members are inactive.

-You MUST be online.

-If you change your Den or create a new one after the Event has started, you will not be able to play the current event.

-You can leave your Den to join another one, or create your own Den before the Event has started without losing the ability to play the event.