Super Robot Taisen Compact 3 is a strategy game set on a fictional planet called Earth, where an alien invasion has occurred. The player takes control of a team of mechs, known as "Robots," which are designed to fight against the extraterrestrial forces. As the story unfolds, the Robots discover that they have unique abilities and strengths that can be used to turn the tide of battle in their favor.
Gameplay involves commanding the Robots in turn-based battles against enemy forces. The player must strategically choose which Robot to deploy, when to use its special abilities, and how to coordinate attacks with other Robots to achieve victory. As players progress through the game, new Robots are unlocked, each with its own strengths and weaknesses.