Arrow keys left and right - Move the Mountain Man.

X or down arrow - Swings hammer. Press and hold to build power, let go of hammer when it is solid red for the most power/biggest boulder.

As the boulder goes down the mountain you can control its direction left and right as long as you have rage power (indicated in the gauge at the top left corner of the screen). The higher the multiplier number next to your rage gauge, the more control you will have over the boulder.

Smash as many objects/cars/people/animals as you can with the boulder for points. Each stage has a destruction quota that you must meet by decimating a certain percentage of the city buildings below. On each stage you have five tries to meet the quota.

Space bar - Pause. On the pause screen you can press Enter to review the tutorial again or hit Esc to reset.