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How_ Spelunky_ got its procedural 'hook' & actually got finished

We hear it straight from the source.

Simon Carless, Blogger

September 29, 2021

14 Min Read

[The GameDiscoverCo game discovery newsletter is written by ‘how people find your game’ expert & GameDiscoverCo founder Simon Carless, and is a regular look at how people discover and buy video games in the 2020s.]

Welcome to a special edition of the GameDiscoverCo newsletter, folks. This one started with the concept that procedural/roguelite games continue to shine super-bright in terms of game discovery. (Streamers love them!)

And we’re a big fan of the Spelunky series - the inventively brutal 2D platformer which was a modern pioneer of the ‘different behaviors every time for more replayability and fun’ genre. (Also, Spelunky was the first procedural game to play with the ‘Daily Run’ concept, where everyone gets the same seed to compete against each other.)

Do you know where we can learn more about the franchise? Via creator Derek Yu’s excellent Boss Fight Books tome documenting his creation of the Xbox Live Arcade ‘HD’ version of Spelunky. (The game has spawned a well-received sequel, of course, but the original has been converted to a host of other platforms - including Nintendo Switch just in the last few weeks.)

For anyone who didn’t know this book existed, it’s described like this on Boss Fight Books’ product page: “Spelunky is Boss Fight's first autobiographical book: the story of a game's creation as told by its creator. Using his own game as a vehicle, Derek Yu discusses such wide-ranging topics as randomization, challenge, indifferent game worlds, player feedback, development team dynamics, and what's required to actually finish a game.”

It’s one of my favorites from the entire Boss Fight Books series on classic games. I’ve known Derek all the way back into the TIGSource days, and find his design-centric writing about Spelunky - originally released in 2016 - to be wonderfully educational and precise. So I asked Boss Fight’s boss (!) Gabe Durham and Derek if we could do two things:

And they kindly agreed to both! So if you’re a Plus member, the entire Boss Fight Books ‘Spelunky’ eBook is now available to download (PDF, MOBI and EPUB) in the Plus data & eBooks back-end. And… for everyone, here’s two key passages from Derek’s book:

Designing Spelunky’s monsters for ‘complex moments’

In designing new monsters [in Spelunky HD], I not only wanted to add more complex interactions and challenges, but I also wanted to make the world feel more alive. The human mind excels at finding patterns and making connections, so just adding a few variations on existing monsters gives the impression that they have families.

When you see that a tiki man is really a caveman with a mask and a boomerang, you start to wonder if they belong to a tribe where the tiki men are high-ranking members. Other patterns quickly play into that notion, like the fact that tiki men are rarer and only appear in the Jungle, whereas cavemen roam around in other areas, too. Tiki men are already more difficult monsters than cavemen, but these little details cement their elite status and therefore their place in Spelunky’s world.

This “alive” quality doesn’t depend so much on the complexity of each monster’s artificial intelligence. Take, for example, the way players associate the four ghosts in Pac-Man with aggression, ambush, capriciousness, and stupidity.

In reality, the behavior of the ghosts is determined by simple algorithms that target different tiles to move to based on each character’s position. When these behaviors play out together on the same map, however, it seems as though the ghosts are working together, with Blinky chasing Pac-Man into the ambush of Pinky and so on.

I applied a similar principle to Spelunky: Combine simple behaviors to give the impression that the monsters are working together. This not only creates challenging situations, but it also makes the world feel more like a living, breathing ecosystem.

Wherever possible, I tried to add monsters that attack you from new directions, so that when they were paired with existing monsters the attacks would feel coordinated. In the Jungle, for example, the snail blows acid bubbles that float upward - you can often see these floating up from gaps in the floor, making gaps more dangerous to jump over or into.

And in the Ice Caves, the woolly mammoth spits a horizontally-moving freeze shot that creates a cross fire with the UFO’s downward-moving projectile. Both the snail’s bubble and mammoth’s blast are also used elsewhere in the game.

The bubble floats up from acid pools in the hidden Worm level and the freeze shot can be fired from a freeze ray the player can acquire from a shop. Giving its inhabitants a shared language is not just a time-saving measure, but another way to make the world feel cohesive.

One of my favorite Spelunky stories is a great showcase of how simple behaviors can lead to complex moments. It comes from Tom Francis, a former editor of PC Gamer and now a fellow game developer, about the time Tom was in the Black Market and watched a tiki man wander empty-handed into one of the shops.

Tom sees the tiki man pick up a boomerang that’s for sale in the shop. “For a split second, I am amused,” he writes. “He’s going to buy a new boomerang! Silly tribesman, you don’t own material wealth!” But then it dawns on him that something terrible is about to happen, and he scrambles away to a safe corner to avoid what he calls the “shopstorm”:

“All nine shopkeepers hurl themselves into the air and start firing their shotguns in random directions. They kill the tribesman. They kill two other tribesmen. They kill frogs, pitchers, snails. One kills the slave he was selling, another kills his own dog. Two of them throw themselves to their deaths in the excitement. Four of them throw themselves into a pit, where their bursts of buckshot cut each other to ribbons.

When the blasts quiet down, I crawl slowly out of my hiding place and walk carefully through the empty shops, collecting everything for free.

What happened here was: the tribesman walked out of the shop. He walked out of the shop with the shopkeeper’s boomerang in his hand, and he walked out of the shop without paying for it.”

What makes Tom’s story so cool is that a number of disparate systems came together in just the right way to write its plot. First, a tiki man had to lose his boomerang, either by getting hit by something (like a tiki trap) or by throwing it at Tom. Then the tiki man had to walk into one of the Black Market’s shops. Finally, the shop had to be selling a boomerang.

What happened next was the tiki man’s “pick up a boomerang and walk away with it” system met with the shopkeeper’s “get incredibly angry if an unpaid item leaves the shop” system and all hell broke loose. Tom’s thorough understanding of these systems takes nothing away from his fascination with it. Actually, the opposite is true—his understanding only deepens his enjoyment.


Traditional, linear, static narratives will always be important in video games, but these personal tales are the ones that, to me, separate the gaming experience from other art forms. Unlike fan fiction, where the audience is creating stories based on their favorite worlds, game players are living them.

And in the context of these stories, the random number generator is akin to Fate, setting up scenarios that at times seem too incredible to be anything but scripted. No wonder game players are known to send prayers and curses to the “Random Number God” or “RNGesus.”

It’s easy to add more and more things to a randomized game and rely on what I think of as the “free value” that randomization offers. In a game with randomized levels, people will keep playing just to see what comes up.

But to make it more than a glorified slot machine requires putting together a collection of systems and rules that is worth understanding, behind a world that feels interconnected.

If you can manage that, a simple story of rescuing a troll from a pit and making it your friend, an “EPIC MOMENT” when a spider was killed by an arrow trap, or a deadly shopstorm becomes something as meaningful and memorable as hours of dialogue and scripted cutscenes. Sometimes more so.

On the art of finishing a game

In September 2010, I wrote an article for my game-making blog called “Finishing a Game.” It’s a strategy guide of sorts for making a video game, although it could probably be applied to any creative endeavor. The thesis of the article is that finishing is a skill as much as being able to design, draw, program, or make music, and that finished projects are more valuable than unfinished projects.

Most creative people are familiar with the first part of making something, and it’s easy to mistakenly assume that the rest is just more of the same. It’s akin to repeatedly climbing the first quarter of a mountain and thinking that you’re getting the experience you need to summit. Or running a few miles and thinking that you can run a marathon.

In truth, the only way to learn how to summit mountains, run marathons, and finish making games is to actually do those things.

The article consisted of fifteen tips on how to finish a game:

  1. Choose an idea for a game that satisfies three requirements: it’s a game that you want to make, a game that you are good at making, and a game you will wish you had made.

  2. Actually start the damn game. Writing design documents and planning doesn’t count.

  3. Don’t roll your own tech if you don’t have to.

  4. Prototype.

  5. Make sure the core mechanics are fun.

  6. Choose good partners (or work alone as long as you can).

  7. Grind is normal, so factor it into your plan.

  8. Use awards, competitions, and other events as real deadlines.

  9. Push forward. Don’t get hung up on one part of the game for too long.

  10. Take care of your mental and physical health.

  11. Stop making excuses for starting over. Halfway through any project you’ll always feel like you can do a better job if you started over. This cycle will never end until you put a stop to it.

  12. Save it for the next game. Do you have a brilliant new idea that requires extensive changes or pushes back your deadline? Save it for another game.

  13. Being behind schedule is a great excuse to cut unnecessary content.

  14. If you do quit, scale down, not up.

  15. Remember that the last 10% is the last 90%. You’re never as close to being finished as you think you are.

I’m obsessed with finishing as a skill. Over the years, I’ve realized that so many of the good things that have come my way are because I was able to finish what I started. Trigger Happy, my first released game, was small and rudimentary, but it was a significant step forward and gave me the motivation, confidence, and experience to keep releasing. From there, Jon Perry and I released several other small games with Klik & Play, and these led to Eternal Daughter, which led to Aquaria, which led to Spelunky. Gardens and forests.

Irrespective of how big the project was, each one I finished gave something back to me, whether it was new fans, a new benchmark for what I could accomplish, or new friends that I could work with and learn from.

Along the way, of course, are the discards of many aborted projects and failed prototypes, and while my finished games wouldn’t exist without these unfinished ones, I also gained less from them in comparison. Mostly, I found them good for flushing out bad ideas and practicing my programming. Some of them also had parts that were interesting and made it into future games that I released. But they never taught me how to finish what I started or gave me the satisfaction that Trigger Happy gave me.

Eternal Daughter was the first big game that I finished. When Jon Perry and I released it in 2002, it was an early example of an indie “Metroidvania”—a nonlinear 2D platformer that took place in a large, interconnected fantasy world.

After the game came out, there was the usual grumbling in the Klik community about it being overhyped, followed by promises of “Eternal Daughter killers”: games inspired by ED that would eclipse it. And playing the demos, I had to agree that some of them looked amazing. On the merit of their individual parts - graphics, music, and technical prowess - they did outclass Eternal Daughter.

But those demos never became anything more than demos. And not for laziness on the part of the creators, who worked on the games for at least as long, and often longer, than the two years Jon and I spend on ED. But what I saw happen in almost every one of those projects was that once or twice a year a new, shinier version of the same demo would come out.

The graphics would be a little better. There would be some fancy new effects or a new battle system. Sometimes a new area of the game would be showcased. But as the quality of the demo went up, the potential for the full game to be released went down. There seemed to be a strong correlation between the number of times a person started over and the likelihood that the project would never be completed.

The reason why people restart projects becomes obvious once you feel the temptation yourself. At some point in any project, you will look back on everything you’ve done and feel like you could do it all better. Perhaps the code seems like a tangled mess. Or maybe the first area you worked on is not as pretty as the second area because your drawing skills improved along the way.

Not at all coincidentally, this is also around the time that you start to see the vastness of the rest of the project spreading out before you like a wasteland. The one level you’ve made needs to be twenty, and mundane-yet-important things like menu and dialogue systems need to be designed and implemented.

It’s easy, at this moment, to think that if you started over and did things the right way that the wasteland might not be a wasteland but a verdant plain you can stroll across to the finish line.

Inevitably, you will hit that same wasteland again no matter how many times you start over, and sadly, it’s the talented creators that get hit the hardest by this, because they’re the ones that are most critical of their own work. The people working on the “Eternal Daughter killers” weren’t amateurs. They were phenomenal artists, designers, and programmers who just happened to suck at finishing projects.

They obviously learned a lot from reiterating on the same early sections, but they never learned how to navigate that wasteland or overcome that consummate destroyer of dreams: being too much of a perfectionist. As a result, they never learned that with each game you finish, it gets easier to finish the next one, because it feels so good to release something that it’ll motivate you to do it again and again.

When I wrote “Finishing a Game,” Andy and I were working hard on getting Spelunky done, so it was as much a reminder to myself as it was a lesson for others. I thought about Spelunky Classic and how naturally that led into this Xbox version - it would have been so much harder if I had tried to rebuild Spelunky Classic over and over again until it came out as the remake.

[Thanks for reading this far! We’re GameDiscoverCo, and we hope you enjoyed this interlude from your regular game discovery/platform news goodness. One final note: Gabe from Boss Fight kindly gave all newsletter readers a special discount code: GAMEDISCOVER, which is valid for 10% off anything in their store (bossfightbooks.com), if you see anything else you’d like.]

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Simon Carless


Simon Carless is the founder of the GameDiscoverCo agency and creator of the popular GameDiscoverCo game discoverability newsletter. He consults with a number of PC/console publishers and developers, and was previously most known for his role helping to shape the Independent Games Festival and Game Developers Conference for many years.

He is also an investor and advisor to UK indie game publisher No More Robots (Descenders, Hypnospace Outlaw), a previous publisher and editor-in-chief at both Gamasutra and Game Developer magazine, and sits on the board of the Video Game History Foundation.

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