Arquillian

Arquillians are a small sapient alien species from the planet Arquillia.

Overview
Arquillians are a species of hand-sized humanoids with greenish-white skin, a large head, large, blue eyes, and very long arms and legs. They wear a Human-sized mechanical suit, which is used for both protection and movement (also hiding their true identity). Much of their energy goes towards operating the mechanical human suit, but they also have an "autopilot" mode for making their life easier. To get the human suit to work, they have to download software programs to the brain. Too much information and the computer can have a meltdown, resulting in them divulging their true identity or catastrophic damage to the suit. They also apparently possess an extremely powerful weapon capable of destroying planets.

In the movie the MiB need to find the galaxy and return it to the Arquillians, who are threatening to annihilate Earth if it is not returned within a certain time period.