The Fourth Wall is a puzzle platformer starring a young apprentice that becomes a wizard during his journey. Next to moving around and jumping, there is a key gameplay mechanic that needs to be mastered to progress through the levels. Normally he moves through a level that shifts the environment through the well-known side-scrolling mechanic. The apprentice learns how to activate the fourth wall however. By pressing and holding down a key, the scrolling can be frozen and a blue glow appears on the edges of the screen. At that moment he is able to leave the left side of the screen and appear at the right side, and vice versa. The same can be done for vertical movement. Dropping down a pit makes him appear at the top of the screen, similar to the effect of using a portal. This can also be used to jump on the left side of the screen and appear on a higher platform on the right side. There is a restriction however. It can only be done when there is room to appear on the other side of the screen. That way, the fourth wall often needs to be activated at a specific spot by observing the environment, or while jumping, at the moment when the screen scrolls vertically to track him.
In later levels additional elements are introduced. There are keys required to open doors, small animals need to be guided to launch the wizard into the air, and there are moving platforms and laser beams. The mechanic can be used to extend the laser beam to a different area or to duplicate projectiles that have been launched as they no longer reach a wall where they explode. For some hard puzzles it also needs to be activated and deactivated quickly in succession to travel past lava for instance.