This game is just lovely!
I managed to trigger a hang (in the Flash version at least) by dying to a trap after playing a card that permits me to take another action (in this case, a sword with another sword in my hand). It looks like it's waiting for me to play the other sword or end my turn, but I'm dead so I can't.
Edit: Given that the game is (often) deterministic, especially considering how much damage you will take after a given action (e.g. because monsters will get a turn or a bomb/trap will hit you), it might be nice to indicate somehow that taking a certain action will result in your death. For instance, when targeting the effect of a card, it could highlight the target in red or show some tooltip text warning you that such an action would be your last.
To me, this is like the concept of check in chess. There, players aren't even allowed to take an action that would result in immediate game loss, though in this game, actions resulting in death can still make sense if, e.g., you get a souvenir or a few stars to count towards a gift.
Granted, it may be very tricky to even determine if an action will result in death in certain circumstances. For instance, defeating enough monsters to reach the next power-up might let you increase (and refill) your will, but could also easily give you power-up options that aren't able to save you from the immediately following attacks.