There's another write-up about the event
hereP.S. Our BWs may appreciate this bit:
During the event, the entire game is locked in nighttime mode. This is not just a visual effect. All aspects of the game that depend on a day/night cycle are locked to the night side during the event. Enemies that only spawn at night will be spawning continuously during the event. Banisher, The Slayer, and Haunted badges (Hero side) and Pirate and Spectral badges (Villain side) are examples of badges for which hunting will be much easier during the event.
