Commander Keen in Invasion of the Vorticons – Episode Two: The Earth Explodes

The second episode of the Commander Keen series, The Earth Explodes, was released on the same day as the other two installments in the Invasion of the Vorticons trilogy. How does it fare in the face of its predecessor?

Analyzing the Experience

Billy Blaze, better known as Commander Keen – Defender of Earth, has just escaped from Mars and returned home. His timing couldn’t be better, for he managed to slip into bed before his parents noticed his absence. Unfortunately, while en route to Earth, Keen noticed a Vorticon mothership looming above his planet – their turrets aimed at every major city in the world. With not even a moment to rest, Keen vaults out of bed, hops back into the Bean-with-Bacon Megarocket, and heads for the mothership, hoping to disable its deadly Tantalus Ray. If he fails, the Earth explodes. While the idea of not needing to get home in time for school the next day is tempting, Keen decides to save the Earth anyway.

Having been built on the same engine as its predecessor, the gameplay of The Earth Explodes is identical to that of its direct predecessor. It too is a platforming game, which was considered something a rare breed for PCs at the time. Levels are selected on a world map as opposed to forcing a linear progression on the player. Most stages are not blocking Keen’s path, but the ones that are must be completed first before he may pass.

Offering a near-identical experience, one may assume that most of my praise and criticisms I had for Marooned on Mars applies to The Earth Explodes as well. For the most part, that is true, as levels continue to be fairly mazelike, and the controls aren’t exactly what one would call responsive. That being said, John Carmack and his team did make various improvements to the gameplay in between episodes.

To begin with, Keen possesses his pogo stick from the very start of the game. This has two implications on the gameplay. The first is that, obviously, you won’t have to search random stages for it. As a blind playthrough of the original game could have been made unnecessarily difficult without the pogo stick or the foreknowledge of its existence, this is greatly appreciated. The less-obvious second implication is that, because it’s impossible for Keen not to have the pogo stick at any point, the level design is adjusted accordingly. This is quite a departure from the original, which, with the exception of the final stage, was designed around the idea that the player could not have the pogo stick. Platforms in The Earth Explodes are often placed in a way that can only be reached with pogo-assisted jumps, and knowing when and how to use it is therefore more important than ever.

There is also one notable improvement that can be observed as soon as you begin the first stage of the game.

Specifically, the presentation, though still simplistic given contemporary technical limitations, is notably improved from that of the original game. Commander Keen’s first adventure took place on Mars, but you would be forgiven for not knowing that even in light of its title or the layout of the world map. This is because the graphics were so simplistic, that, even with the aliens running about, one could get the impression it took place in any random location on Earth.

Conversely, the graphics in The Earth Explodes do successfully convey the setting with visuals alone. It is a noticeably more mechanical look than that of the Martian landscape with metallic walls and maintenance robots walking on the platforms. It’s subtle, but this does have a definable impact on the gameplay, as Keen must occasionally make use of the robots’ patterns to reach platforms he couldn’t on his own. It’s also helpful in the sense that, by having a better presentation, the potential hazards generally look more dangerous than those on Mars, thus preventing any unexpected deaths before they can occur.

With a new scenario comes a new goal for Commander Keen to achieve. Equipped with the Tantalus Ray, the Vorticon mothership is targeting eight cities on earth: Paris, Cairo, New York, Moscow, Sydney, London, Rome, and Washington, D.C. The Tantalus Ray has its own outlet for each target hidden in eight of the game’s sixteen stages. The power source for each ray can be destroyed with a single shot from Commander Keen’s Raygun. This proposition can give one the impression that it’s possible to complete the game only having saved a handful of cities and, in turn, receiving a less ideal ending. However, this isn’t the case. Taking cues from its direct predecessor, all of the stages directly relating to Keen’s goal must be completed. In addition, two stages actively block his progress. This means that in total, ten stages out of sixteen must be completed in order to win the game.

This aspect by itself goes a long way in addressing the biggest problem with the original game in how a majority of its stages were pointless filler. If you knew what you were doing, you could get away with only completing six of the sixteen stages. With the series’ second episode, Mr. Carmack and his team made a greater portion of the stages mandatory. This ensures that the player actually has a motivation to engage with the material.

The level design itself is a marked improvement over that of the original. One curious aspect of this game is that cans of soda now serve as platforms if Keen jumps on them. They can still be collected for points like other food items, but in order to do so, Keen must approach them from below or the sides. In a few stages, you can manipulate the paths of the maintenance robots by collecting these cans so they won’t be blocked. Alternatively, they serve as barriers to prevent Keen from entering certain areas too early. It’s questionable whether or not this is even intentional given how absurd the concept is, but it does add puzzle elements to the experience. Knowing when and how to remove the cans is often important to reaching the end of some stages.

Lastly, as a possible result of making so many stages mandatory, The Earth Explodes does follow a more natural difficulty curve than its direct predecessor. In Marooned on Mars, only the intended final stage was noticeably more difficult than the remaining fifteen. Even then, the most difficult part of the stage was finding out that the Vorticon commander guarding the Everclear bottle can only be defeated by dropping a large, stone slab on top of him.

This isn’t so in The Earth Explodes; the final stage is a grueling gauntlet that serves as a final exam for the rest of the game, involving jumps onto moving maintenance robots and breaking past a tough security unit. Elite Vorticon soldiers patrol the halls of the mothership, often guarding the devices powering the Tantalus Ray. They require three shots to kill and are capable of shooting back with their own Rayguns. Trying to face them head-on is usually a death wish, but as it turns out, Vorticons are incapable of jumping in darkness. You can use this to your advantage by turning out the lights in a stage. If you’re not privy to this fact, you will die countless times until you learn their weakness.

Unfortunately, as much of an improvement The Earth Explodes manages to be over Marooned on Mars, having been built on the same engine ensures the first episode’s problems return for an encore performance. The controls are as bad as ever, Keen still can’t take a hit without dying, and its myriad shortcomings all cover up for the fact that the game is incredibly short. In fact, many of the problems plaguing the original game are markedly worse in this installment.

The original game’s bad controls weighed the experience down, but because the enemies Keen faced were non-threats once you learned how to deal with them, the flaw wasn’t as noticeable. The simple presence of the Vorticon Elites highlights just how poorly optimized the engine is at handling enemies capable of shooting back. Once again, Keen does not jump as soon as you press the appropriate action key, instead bending his knees for a brief second first. This split-second-long amination can easily cost you a life if Keen gets involved in a shootout with one or more Vorticon Elites.

While Keen can fire a single shot while airborne, he is not capable of jumping when he has his Raygun drawn. Firing a shot requires the player to press two keys while holstering it can only be done once they’re released. Tying into the problem of requiring two keys to be pressed in order to fire the weapon in the first place, and you can forget about jumping out of the way of an incoming projectile under most circumstances. It is nice that the game provides players a way of significantly reducing the threats of its most powerful enemies. On the other hand, with this bit of context, it feels as though the team realized just how absurdly powerful the Vorticon Elites were halfway through development, but rather than reprogram them to be easier to fight, they merely implemented a debug trick in the final product to hastily patch the problem.

Drawing a Conclusion


  • More required stages
  • Improved presentation
  • Slightly better level design

  • Slippery controls
  • Fragile protagonist
  • Short
  • Annoying sound effects
  • No music

The Earth Explodes makes for a somewhat interesting case study on the heels of its direct predecessor. Although released on the same day as Marooned on Mars, it does show a bit more ambition than the original game, which, in hindsight, came across as a basic technical demonstration for what Mr. Carmack’s scrolling engine could do. This time, there is a tangible cohesiveness to the level design, and that goes a long way in making The Earth Explodes feel like a game in its own right. However, while this ambition does result in a slightly improved experience overall, it also highlights the engine’s shortcomings in ways the original game didn’t. To put it another way, the developers enhanced the original’s strengths while bringing all of its weaknesses along for the ride.

The result? A game that is every bit as difficult to difficult to recommend as its predecessor. Just like Marooned on Mars, The Earth Explodes was released in a time when, partially thanks to the medium’s decentralization, it did not have any meaningful competition on its platform. Similarly, while its place in PC gaming history is a secure one, it’s not really something anyone outside of historians should look into. It is impressive how there was measurable artistic growth in between episodes, but it’s still not an effort that has, in any way, stood the test of time.

Final Score: 3/10

2 thoughts on “Commander Keen in Invasion of the Vorticons – Episode Two: The Earth Explodes

  1. With all the changes in there, it does sound like they much improved on the original. Although even those improvements just seem to bring those features up to par with other console platformers of the time, so that only goes so far. Those controls though. No matter how good the rest of the game is, there’s no getting around those controls. I said it last time, but it’s crazy to me that they had a whole keyboard to work with, and decided not to use a third button there. Seems so basic.

    Liked by 1 person

    • I wouldn’t say it’s a significant improvement over the original, but it does edge it out by virtue of having a bit more focus and not making half the game optional. It still gets outclassed by even the mid-level platformers you would find on consoles, however, which is at least partially a result of making the player push two keys to fire the weapon – something that was completely unjustifiable even back then. I think the thing is that developers back then, having not grown up with the medium, simply did what made sense to them, not thinking about if the players would find those choices intuitive.

      Liked by 1 person

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