Good question. The short and sweet answer is that this is a party thrown by the Ministry of Magic to honour the promotion of Lord Borr within the Ministry of Magic. If you work at the Ministry, you were given the day off to attend this event. There will be announcements made that will affect all of the Wizarding World, so stay tuned in.
The event, held just outside Gringott's Wizarding Bank, is being housed in a GIANT outdoor tent. Have your character
check in with Security, grab a
bite to eat, and
socialize ALL you want. Most importantly,
listen for important announcements from Lord Borr and his associates.
You may play more than one character at this event. You SHOULD bring as many characters as you can to it, even. Fliers announcing the event have been around Diagon Alley and the Ministry for some time now, and even a few Hogwarts professors and students are due to drop in (students are allowed by invite only!).
Feel free to jump right in.
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What is this? 
