The Sentinel

The Sentinel is a defense game in which you control a cannon atop a castle and try to withstand rising waves of balloons. You choose upgrades to strengthen your defenses, improve your weapons and abilities, and keep the castle safe.

Control the cannon

The cannon fires spheres continuously, and you move it with the keyboard arrows. The spheres fall under gravity and collide with balloons rising up the screen. Each balloon displays how many hits it needs to burst. When a balloon reaches a certain height, its displayed value is deducted from the cannon’s life count.

Choose upgrades

At the start of a match, you choose one of 20 available upgrades. A bar at the bottom of the screen fills over time; whenever it is full, you can choose another upgrade. Your choices let you reinforce defenses or focus on attacking dangerous enemies before they get close.

The match ends when the cannon’s life count reaches zero or when you survive enemy waves for 15 minutes. Points earned during matches increase how many upgrades you can choose at the beginning of future games, from one up to a maximum of 10.