CrystAlien

The CrystAliens are a hostile race that have invaded planet Mars.

History
It's stated that the CrystAliens are not from Mars but came to Mars to conquer it in order to obtain the abundant Energy Crystals (Brickonium) deposits on the planet. In LEGO Battles their ship is shown crashing on the Martian surface. They enter an armed conflict with the astronauts on Mars. In neither game are the Martians shown leading to various speculation from the series being in a different universe, to the Martians being a conquered people or even extinct though it's more likely that the CrystAliens have begun their invasion around Human colonies as the Martians would pose more formidable fortifications. It's likely that the present monarch of Mars (probably Riegel) has gone into a defensive mode and is perfectly fine with having troops stationed to defend Martian settlements (and crystal reserves) without concern for what becomes of Human settlers. He is after all under no obligation to protect Earth's holdings on Mars despite what a CrystAlien victory will mean for his people. This is of course mere speculation for as stated, we don't see any sign of the Martians.

Government
The CrystAliens are organized in a hive society but not under a hive mind. The CrytAlien monarch is a multiple legged almost arachnid Queen who manages their civilization through various 'Commanders' who operate individual hives. It was in fact a commander who crashed on Mars, and upon discovery of Energy Crystals summoned an invasion force (LEGO Battles).

Physiology
CrystAliens are shown to be a transparent or solid green and to have glowing eyes with all but the Queen possessing green glowing eyes. They do not actually give their species name in dialogue though the Astronauts refer to them as CrystAliens due to their crystal like bodies and motivation to acquire Energy Crystals. Drones, the worker caste of their society have a hole through their chest which is used to store them in Hives (via a rack). They are the only ones with this hole and have used it for storage.

Technology
CrystAliens are air-force oriented when it comes to military tactics with jets, fighters, and drop ships making up the bulk of the invasion force. Infantry, save in numbers, is a weak point for them as they are armed with energy staffs capable of shooting energy blasts (energy presumably of Crystal origin). To compensate for their weak ground forces they make use of infiltration and sabotage before an assault.