The astros of Earth Command travel to Mars to explore the red planet and mine for Power Crystals. Although the Red Planet appears barren at first, they soon come in contact with hostile alien lifeforms attacking their personnel and vehicles. To defend themselves, the astros quickly militarize, turning their mining vehicles into battle tanks. As the war continues, the astros eventually discover the Alien Hive. However, when the Alien Commander emerges to lead his troops.
The story of Mars Mission was largely documented through the online Real-Time Strategy game CrystAlien Conflict, in which the player had the option of playing as either the astros or the aliens. In 2009, Mars Mission was featured prominently in the Nintendo DS game LEGO Battles, where again the player could play separate campaigns for Earth Command and the aliens.
LEGO Mars Mission is often considered a Spiritual Successor to LEGO Life on Mars, the last LEGO Space theme since LEGO acquired the Star Wars license. Whereas Life on Mars was notable for showing peaceful relations between the human astronauts and native Martians, Mars Mission started the trend (to be followed by LEGO Space Police, LEGO Alien Conquest, and more) of heroic humans battling evil aliens.
LEGO Mars Mission contains examples of:
- Action Girl: Gemma. In LEGO Battles, she is the only female Hero Unit who is playable in the main story campaigns.
- Affirmative Action Girl: Mars Mission had no female characters (outside of a "Miss Bell" mentioned in one of the transmissions), so LEGO Battles introduced Gemma for Earth Command and the Alien Queen for the aliens.
- Alien Abduction: Inverted. The astros frequently capture aliens and bring them back to the lab to study them.
- All There in the Manual: The majority of the theme's storyline could only be found through the website, which had transmissions from the astros in addition to the CrystAlien Conflict game. Before LEGO Battles, there was only a single promotional material which revealed that the aliens are not native to Mars.
- Book Ends: The opening and final cutscenes for the alien campaign in LEGO Battles shows the Alien Commander building miniature LEGO sets on the ETX Alien Mothership's bridge.
- Chew Bubblegum: The aliens' Special Ops level in CrystAlien Conflict "Commander", in which you play as the One-Man Army Alien Commander, begins with the message "I'm all out of bubble gum!"
- Composite Character: In the second wave of LEGO sets, the astros received a pair of little Robot Buddies. In LEGO Battles, the designs of the two robots are merged into a single Surveillance Robot.
- Continuity Nod: The astronauts have the Classic LEGO Space badge on their uniforms.
- Color-Coded Armies: The Astronauts are white with orange highlights and blue energy weapons, while the Aliens are black with green highlights and energy, plus a smattering of red.
- Cool Starship: The astros have a number of cool ships, including MX-71 Recon Dropship, Starship 1, and MX-81 Hypersonic Operations Aircraft.
- Crossover: LEGO Battles featured a crossover between LEGO Mars Mission and LEGO Space Police, with several members of the Black Hole Gang taking refuge on Mars and going to the aliens for protection from the Space Police. The alien army also has a few units from the robot army from LEGO Exo-Force. There are also a number of references to classic LEGO Space themes: the skeletal remains of a Blacktron: Future Generation astronaut are found on Mars, Earth Command's Worker Unit is based upon Ann Droid from Exploriens, and Earth Command's Mission Control is Commander Cold from Ice Planet 2002. Additionally, since LEGO Battles features LEGO Castle and LEGO Pirates, even more crossover opportunities are available via Free Play mode.
- Drill Tank: The MT-51 Claw-Tank, MT-101 Armoured Drilling Unit, MT-61 Crystal Reaper, and MT-201 Ultra-Drill Walker are all massive mining vehicles equipped to defend themselves from alien attacks.
- Everyone Calls Him "Barkeep": Everyone (except for Biff Barker, Commander Galaxy, Gemma, and Biff) simply goes by their occupation, such as Miner, Gunner, Dropship Pilot, etc.
- God Save Us from the Queen!: The villainous Alien Queen from LEGO Battles.
- Hero Unit: In LEGO Battles, Gemma and Biff are Heroes for Earth Command while the Alien Commander and Alien Queen are Heroes for the aliens.
- Humanoid Aliens: Although the aliens are a major departure from the standard Minifigure design, they still are humanoid with two arms, two legs, etc. That is, with the exception of the Alien Queen.
- Insistent Terminology: The Aliens are Aliens, not Martians, as they aren't actually Martian natives, but just here for the Crystals, same as the Astronauts, with the implication that they wiped out the Martians of Life on Mars beforehand.
- Martians: Subverted. Despite what one might expect from a story about battling alien lifeforms on Mars, the aliens are not actually native to Mars; LEGO Battles makes it explicitly clear that they are just as alien to Mars as the humans are. Although the friendly Martians from LEGO Life on Mars are sadly nowhere to be seen, LEGO Battles does hint at the existence of Martians by showing ancient ruins on the planet, dating back long before the arrival of the aliens or humans.
- Mineral MacGuffin: The Power Crystals. Even more so in LEGO Battles, where both armies are often seeking out ultra-powerful purple crystals, which produce ten times as much energy as the normal green crystals.
- Mini-Mecha: The Robotic Mining Mech, retooled as the Gripley in LEGO Battles.
- Mission Control: Commander Cold for Earth Command in LEGO Battles.
- One-Man Army: The Commando Drone in CrystAlien Conflict, which has greatly increased health, speed, and firepower. When Special Ops were released, the Drone was replaced with the Alien Commander, who functions exactly the same.
- One-Steve Limit: Played with. There are two separate characters among the astros who have the given name Biff: the Claw-Tank Driver and Earth Command's Hero Unit (who has the same face as the Astro-Pilot). However, the two characters are never shown together. This isn't even counting Biff Starling, one of two LEGO minifigures who were actually brought to Mars by NASA in 2004.
- Only Six Faces: The astros reuse faces of minifigures from previous LEGO Themes. For example, the Astro-Pilot and Biff use the same face as the Scorpion Palace Guard; the Dropship Pilot and Commando use the same face as Dash Justice; and the Trike Driver uses the same face as Specs.
- Pardon My Klingon: In LEGO Battles, the Alien Commander frequently curses with "ziff".
- Power Crystal: Both armies mine Mars for energy crystals which power their vehicles.
- Real-Time Strategy: Not just once but twice, with CrystAlien Conflict and LEGO Battles.
- Recycled Title: "Mars Mission" was previously used by LEGO as the title of a Space Port Master Builders kit.
- Series Continuity Error: The storyline in LEGO Battles contradicts previously-established material such as CrystAlien Conflict.
- Shout-Out: In CrystAlien Conflict, "beeblebrox" unlocks many cheat codes, and the aliens' Special Ops level can be unlocked with either "t2000" or "theylive". See also Chew Bubblegum.
- Spider People: The Alien Queen, whose body from the hip down is modeled after that of Spy-Clops.
- Spider Tank: The MT-201 Ultra-Drill Walker combines this trope with Drill Tank.
- Tank-Tread Mecha: The MT-51 Claw-Tank and MT-61 Crystal Reaper are both treaded tank-like vehicles that are also equipped with arms and hands, giving them the appearance of mechs.
- Transforming Vehicle: The MX-41 Switch Fighter can transform between a rover and a spacecraft. Its design and transforming function was integrated into the Starfighter in LEGO Battles.
- Whole-Plot Reference: Crystalien Conflict is one to Command & Conquer, with many of the latter series mechanics and UI features mimiced. The fields of green crystals standing in for Tiberium, and a surprisingly complete mimicry of Command And Conquer's tech tree.
- Worker Unit: In LEGO Battles, both armies have a Builder unit that can gather resources and speed up the construction of buildings and other units. Earth Command's Builder is modeled after Ann Droid, while the aliens' Builder is the Battle Arachnoid mini-bot.
