P.O.D.

 (Planetary Orbital Defense) is a badged game on Kongregate. The game was subtitled Zoids - Planetfall after a big update that added difficulty settings, added a new enemy and fixed glitches. This game has roots on the old arcade game, Space Invaders.

Controls
Use the mouse to aim and shoot. "A" activates the player's power-ups. "S" selects power-ups. "D" selects tanks. To move the tank, pressing "Z" makes it go left, and pressing "X" makes it go right. To pause the game, press "P", or, to reset it, press "CTRL". Pressing "0" toggles help on/off.

Keys are fully customizable.

Gameplay
The game presents three difficulty modes: Easy, Normal and Insane, as of the last update. The player is controlling a massive pink gun used to destroy invaders, and eventually, the scenario changes so the player can now control more guns, pressing D to change between them. It is vital to complete the game.

Throughout the game, various capsules appear on the sky, and if the player shoots at one of them, they get a power-up, which are an extremely useful tool against the invaders. If any city gets destroyed by the aliens, it's Game Over. When an alien hits a building, it loses life, which is recharged over time, however, if it goes down all the way to zero, it is forever lost.

The game ends on Level 15 in a final showdown against their Mothership.

Plot
The player's home planet is being massively invaded by evil aliens, who come in a variety of forms, from floating squids to very mechanical droids. You take control of a gigantic weapon that shoots dozens of rounds per second, and your mission is to protect the cities of your world from being infected and destroyed by the hostile visitors. In the end, the player destroys the Alien Mothership and your world is now free from harm.

Trivia

 * This is one of the lowest rated badged games on Kongregate.