Nvm I'm a goof
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I've had several instances of simply losing my ability to dig in Graveyard. I'm not hitting obstacles, I just simply can't dig or climb up. I don't see any particular reason for it, it's happened on the easy and medium difficulty and on various levels.
I apologize if this is a known issue or a mistake on my part, I didn't see anything about it in the forums or any particular pattern in my games.
Is it because you're running out of moves (or shovel points or whatever)? You only have a limited number of times you can dig before it won't let you anymore, although there is a powerup in the game that gives you a few extra moves.