Board Thread:Help!/@comment-13634584-20150313231503

I got this weird medallion. I don't really remember what it's called, and for a few months i didn't seem to be able to use it.

Today i tried to use it and it summoned an event called Frost or Treat. It's a frost/pumpkin moon hybrid, and i would like some help because i don't know how i got the medal, and why i couldn't be able to use it (it was around December to February). I need some help, and i would appreciate if someone could explain. 