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Man Eaters from Planet Tetravenus revolves around one core mechanic: energy. Energy not only acts ammunition, running out of energy means you lose the ability to move until your energy comes back online. Instead of damage being tied to a separate stat, damage reduces your maximum energy, which means you can fire less bullets, and lose the ability to move even quicker.

Energy is used for even more things then that however. At the end of each wave you're given the option to purchase an upgrade. This will reduce your maximum energy, but make you more effective. In lieu of this, you can get a boost to your maximum energy.

Enemies also serve two purposes. Not only do they threaten the player, they also drop energy when they die, which restores some of your current energy, allowing you to continue firing for longer.

These little energy drops also not only restore your current energy, if you're at full energy, they give you back a bit of your max energy.

Third-party resources
Monogame: https://github.com/MonoGame/MonoGame/blob/develop/LICENSE.txt

Contributors
Ross Kilpatrick
Nicholas Walton