I would say the one big thing missing is the motivation of the player: if it was “me” in this situation, wouldn’t you just get away as fast as possible? Why not take it a step further: you have this ability and have been hiding out of town (BTW, how do you survive/eat/drink? some metaphor needed there), but something is threatening the city that only you can destroy, and so you are trying to do that with minimal collateral damage? So, you are forced to be in the city, but must minimize your damage while destroying something else?

Prototyping the movement and actions, and how the destruction would work, is a good plan. I would like to know more detail of what kind of controls you are thinking about, what kinds of movement and so on, so we can judge success!