Smithereens! takes place in a time when knights were bold and castle crumbling was one of the most popular sports. In this Artillery clone, two players must try to destroy each other's castle with their catapults. By pressing any direction in the joystick, the player launches a boulder toward the opponent. The longer the stick is held, the farther the boulder goes.
The gameplay revolves around launching boulders at each other's castles and soldiers, trying to get points by hitting the enemy or their own castle. Players score three points for each hit on a castle, seven points for hitting an enemy soldier, and ten points for hitting an enemy catapult. The winner is the one with more points at the end of ten battles.
The game also features three variations in catapult tension, which affects how fast the catapult shoots boulders. With higher tensions, the catapults become faster, making the gameplay even more challenging.