Sentinel is a side-scrolling action game where an alien attack has devastated several worlds. You must rescue them by using the Sentinel , a glowing orb that can absorb alien energy, to destroy enemies and enemy fire.
The Sentinel floats above the scrolling landscapes, and you must use the light gun to protect it from attacks. If an enemy is not destroyed, its energy will deplete the Sentinel's supply, causing it to be destroyed. Along the way, you may encounter bonus capsules that contain increased firepower and energy, helping you on your mission.