How do you get the Fall Theme, i heard there was one. Also are there any other hidden themes? Thanks!

The Morostide theme comes from the pumpkin carving achievement (carve 500 pumpkins)

There's also a Luminaire theme that comes from the Free all the Fairies! acheivement (free 1000 snow fairies)

As far as I know those are the only unlockable site themes.

The Fall theme is from giving 1000 items to the Red Rreign during Fireside, if I remember correctly.

Awesome yay! Thank you! I love the hidden themes!