Your goal in this competitive game of timing is to knock more blocks from the Stack than your opponent. To achieve this, all you need to do is hold down the fire key ("A" KEY for player 1 or "L" KEY for player 2) to charge your cannon, and then release it to fire at an active (green) block. Repeat this process until you knock the block from stack. If your opponent knocks the block from stack first, you lose! Good luck!