This game has a lot of potential if you decide to continue with the project or idea because the mechanic of building your own monster by digging up the parts is fun.
I know that you guys made each round last as much as the song, but it felt a little abstract in game. I think you could have police or something be the threat if you don't make it in time. Other than that, I think that the time limit fits well with the There and Back again theme, as it makes the going back in forth a gameplay factor in your race against time. Some of the collisions with the trees and gravestones were a little wonky, which made traversal a little annoying.
Diggenstein is a cool game with a cool mechanic, and I think it has the potential to be expanded upon.