Ok, so my players encountered a Grave Knight, which they defeated, however none of them made the necessary knowledge check to know about the supernatural rejuvenation ability. Believing the armor to be simply magical, they stuck it in their bag of holding. In a few days the Grave Knight will be fully healed and rejuvenated inside the bag. Since the Grave Knight is undead, I am concluding it can survive in the bag of holding. Here is where I feel it will get funny.
Can the Grave Knight escape the bag on his own? Or can the Grave Knight attempt escape any time the bag is opened (to retrieve or place an item in the bag)?
I'm open to suggestions and ideas on this. It will be a complete surprise and very comical because they have no idea.