Stack of Defence is a unique mix of a physics-based puzzle and action/defense game. Each level begins with you stacking various blocks, some of which will fire at enemies. Keep in mind that you're being timed during this building phase. Once you have stacked all of your shapes or the timer reaches zero, the defense phase begins! In this phase, you will need to shoot enemies and use your special abilities to prevent them from breaking through your defenses. Your special abilities include repairing blocks, sacrificing blocks to recover HP, making blocks temporarily invincible, poisoning enemies, freezing enemies, launching rockets, and dropping bombs. These abilities and various upgrades can be purchased between stages.