At night time, villagers (that have a profession) will have a button in their inventory that will give you a Surprise Trick or a Treat!
Have fun finding out what you get!
Treats are Edible Candy Items, some may give you buffs!
Tricks are small annoyances that may or may not hinder your gameplay a little bit!
(This is intentionally left a bit vague because the fun is in the surprise just like on halloween!)