Basic idea.  First month, October (Grounded meets Goosebumps).  Add a lunar cycle with a semi-rare RNG where a full moon "might" spawn a seasonal side quest + structure in a non-buildable area each time after sleeping.  Quest could include multiple objectives and a boss fight that would yield "Halloween" style cosmetic skins (or functional rare gear).  Rinse and repeat for any given holiday/event.

 

Hey all, just signed up with an account.  I see a message that I need to be approved by a moderator.  Any help would be appreciated, thanks.