Basic idea: Using a massive projection and scrambler technology based off basic cloaking systems. You can mimic a moon orbiting your planet. Giving the ability to hide and trick your foes into seeing something that is not really there.

Size: 2
Game bonus: X cloak and X defense (up to dan and crew or can even be based off of the size of the planet)
Limit: No idea could be based off the size of the planet.

This to me could even be made into a new tech tree or if anything a very cool artifact building to place on your planet.

Sounds good, except if you get attacked by Saiyans you're boned.

Well every tech should have a drawback so that you have to balance fantasy against practicality, anything that makes someone or something all powerful just takes the fun out of the game.