You need to collect a lot of guild stones to unlock exclusive items. For example 1 million stones. If you didn't unlock the event guild hall before the events end - you can continue in the next year. Guild stones should be more useful +-
Imagine ice guild hall for the WT, spooky hall for the BM, factory for AM, castle for DT and so on. And you need to unlock it in 45 days (Or depends on how long the event lasts) or you'll continue it in the next year
||But please, make it as a challenge and not as a $ deal||