Warning: Spoilers for season 1 of Invincible ahead.
Amazon's Invincible season 1, episode 4, "Neil Armstrong, Eat Your Heart Out" gave audiences a glimpse of what the universe's Mars was like — but, there was a lot that about the red planet that wasn't included from the comics. The events of episode 4 come from Invincible Issue #18, and much of the episode's plot comes straight from the comic (besides the design updates the Martians and their weapons received). However, there is more to everything Invincible has shown so far.
In Invincible episode 4, Mark is assigned to secretly travel on a mission to Mars in order to make sure everything goes smoothly. Cecil was expecting a possible interference from the Martians, and he wanted Mark there to deal with it should anything happen while giving humanity the space to make an achievement on their own. When Mark falls asleep on the job, the astronauts were taken by the Martians to be executed to prevent the spread of the Sequids, a small species that take over host bodies and operate them through a hive mind. The Martian Emperor is impressed to find that Mark is not affected by them, but still insists on killing the humans. Mark manages to escape Mars with the astronaut crew, leaving the Martians to handle the Sequids themselves.
There are still open questions about Mars that Invincible season 2 can address: what is going to happen to the planet now that the Sequid attached to one of the human astronauts? Why would one of the Martians disguise themselves to replace a human and travel back to Earth? If the Coalition of Planets and the Viltrum Empire come to blows, where will Earth's closest neighbors stand— or will the reclusive society make a stand at all? During the brief teaser for season 2 at the end of episode 8, there is a glimpse of the Sequids, meaning it's likely viewers will be seeing them again very soon — until then, here's everything about Mars the series left out from the comics.
The Sequids Are A Slave Race
While Invincible tells us plenty about the Sequids' abilities, little is said to their backstory in the animated series. In episode 4, the Sequids are treated as a dangerous pest — but in Issue 18, the Martian Emperor reveals that the Martians have been using the Sequids as a slave species for hundreds of years. He describes them as "easily manipulative" and "easily conquered." Through advanced breeding, the Martians have been producing stronger and stronger Sequids over the centuries. In the comics, the Martian Emperor isn't worried about the Sequids finding a host because they're a danger to the universe — but because they'd be a danger to Mars. He explains to Mark that the Sequids would surely overthrow the Martian government if they ever found a host, which is why the humans (or "solids") could not be allowed to live. This narrative has been left out of the animated series. Instead, the Martians claim they are preventing global destruction by keeping the Sequids on Mars; whether or not this is true remains to be seen.
The Martians Are An Advanced Society
Invincible season 1 gives audiences a view of Mars' underground society in the animated series, but Mars has gotten a major redesign from the comics. In Issue #18, readers are given hints towards how developed Mars is: as Mark is led down into Martian territory, it's a fully developed interior, filled with pipes and vents (and Sequids clearly at work). In the animated rendition, Mark instead finds a dark, primitive-looking tunnel overrun with Sequids. In Issue #18, the Martians display their teleportation technology and discuss how they've bred the Sequids into the perfect slave race; the animated series doesn't show this level of technology, and the Martians are shown more as a naive race with technology more on par with Earth.
The Martian spears, though re-designed from the comics, are one of the few pieces of technology that have crossed over from Issue #18. The Emperor's design in the comics more closely mimics those of the guards — he's an intimidating, muscular man who looks ready for action at any moment. In the animated series, however, his garb is more papal in nature, and he strikes a much less intimidating figure. This complete overhaul on the Martian Emperor and Martian Society may mean they have a different role to play in future seasons of Invincible.
Mark Puts Up A Bigger Fight
At the end of the Mars mission, Mark and the astronauts have to retreat in order to escape execution. Martians on the backs of beasts run them down across the arid planet, and electric bolts fly across the sky behind them — and when Mark tries to take them on in a fight, he's quickly sent out with his tail between his legs. The fight at the end of Issue #18 of Invincible sees Mark being able to hold his own against the Martians; he's able to blast through groups of them and take a few of them one on one. This difference may be because the Mars mission happens at a different point of the timeline in the comics. By Issue #18, Mark has already confronted Omni-Man, started working for Cecil Stedman, and begun college; in the animated series, it happens relatively early on in terms of Mark's abilities. Because of this timeline discrepancy, it makes sense that Mark is a little in over his head in episode 4 as compared to the comics.
The Martian Shapeshifter Reveal
The end of episode 4 gives audiences only a tease to allude at something the Invincible comics confirm. As the astronauts are retreating from Mars, one of the astronauts' American flag patch moves on its own. As the camera pans down to the surface of Mars, it's revealed that that same astronaut has fallen victim to the Sequids — so who is on the ship? Fans of the comics would know that the imposter aboard the ship is a Martian who has shifted himself to resemble Rus Livingston, one of the astronauts on the Mars mission.
Issue #19 follows Rus back home after a "successful" Mars mission, but behind closed doors, Rus's vissage gives way to the Martian's natural state. At this point in the comics, it isn't explained why the Martian has come to Earth — but, the comics do confirm his presence on Earth will the animated series has not so far. With Invincible being approved for seasons 2 and 3, there is hopefully more about this fascinating civilization to come in future episodes.