The Onyx Gate Tower is an odd supernatural phenomenon that occurs at The Tower under certain conditions.
The Onyx Gate Tower is very similar to The Tower, being transformed from it by unknown forces. Between the dates of September 6th and October 31st, the sky around the structure will darken and a mysterious green light will shoot upward from the roof. The occupants inside seem to be unaware of this change.
Currently this event is limited to a holiday special taking place from early September throughout October. While the area itself is accessible without any additional items or puzzle solving, there is no special interactivity that can't be done under normal conditions. The only change that occurs is if the player has The Rose Bead in their inventory.
In addition to housing all the usual guests in The Tower, the player can use this area to access Rose's private home in Denver. Once the player has The Rose Bead in their possession, a portal will appear above the tower.