I am done chasing that darn donut dog.

Congratulations! You have found one of the secrets in this game where "Difficulty is greatly increased when Dachs is on the map. Let him flee or use hammers to slightly decrease the difficulty."

Do you folks really think that there is something like a “difficulty setting” that is set to “more difficult” when you have a Treasure Chest and Dachs has appeared with the key? Any evidence of that?

I rather like Dachs and would be disappointed if his appearance would make CCFS levels harder! But @hdfj123 says above, once you have the mystery chest you do get to keep it forever until you finally get a chance to catch Dachs and get the content of the chest.

I agree with @MountainMom that I have not noticed any systematic differences in difficulty when Dachs was present and a Mystery Chest was offered. However, once a Mystery Chest is offered, there usually there is a 2-hour time limit to progress through the next several levels to get to Dach who has the key to open the Mystery Chest and get the rewards. I find it is harder to play well when you have a time limit like that (possibly because you are hurrying and not making each move as good as you can), and that time pressure may make the next few levels SEEM harder. Good luck getting Dachs and his key for your Mystery Chest!