I used kick addon to open the door which is usually locked (I'm talking about the house which is near the place where the boss fight is) and then entered the house with full interior. Then I went out onto the main road and turned right. There I saw some kind of bag and it was glowing. When I picked it up, a message appeared. It said, "Hidden bag of treats found." Can anyone tell me what it is? I've already checked if there're some new bonuses but no. I hope I get answers to this question.