Rainbow Speed has been released
Hi, this is Yuu!
The game I wrote about two weeks ago, featuring a unicorn and a rainbow, has officially been published on js13kGames!
Rainbow Speed
Leap from cloud to cloud as a unicorn, weaving an unbroken rainbow trail.
This time, I’d like to write about the journey of bringing the game to completion.
The 13KB Limit
First of all, the js13kGames submission period is about one month, while I managed to complete this game in about two weeks. The actual development time was even shorter than that.
Even so, seeing that more than 30 games had already been submitted before mine, I feel that deciding to submit with some time to spare was the right choice rather than waiting until the very last minute.
The reason I was able to finish the game in such a short amount of time is that 13KB is surprisingly small.
As I mentioned in my previous post, when working with such a strict size limit, it’s more important to figure out what you can remove than what you can add.
In my case, the image data alone ended up taking up nearly half of the available space.
Still, I think I managed to make the unicorn itself quite cute and fun to control.
I also liked the top-down version of the unicorn I made previously, but I’m personally much happier with this version since I was able to use a side view and add animations.
The 2026 theme is “Unicorns and Rainbows,” and with that combination, I think it’s only natural to think of Rainbow Dash from My Little Pony.
Since figuring out how to use the unicorn was an important part of the game, I was also interested to see how other entries interpreted the rainbow theme.
It’s a simple action game that can be played using only the jump button, and I think the theme itself is fairly straightforward. Still, I feel I managed to strike a good balance between the size limitation and how the game feels to play.
At this point, the game was 13,298 bytes.
For reference, js13kGames treats 13KB as 13,312 bytes, so I still had to squeeze out a little more space.
After optimizing the sprites and changing the title, I managed to bring it down to 13,294 bytes.
Changing the Title Right Before Submission
I actually submitted the game on Thursday night (August 27).
However, right before submitting, I discovered that another entry had the same title, so I had no choice but to change the title before submission.
Personally, I wish there had been a feature that could check whether your title was already being used by another entry before submitting.
Still, I was able to submit the game successfully.
Adding Wavedash
During this game jam, I also discovered a platform called Wavedash, so I decided to take the opportunity to integrate it into the game.
…And this made things even more painful.
When I tried adding features such as a leaderboard and achievements, I ended up about 130 bytes over the limit.
The Wavedash integration itself was surprisingly small, which was great, but simply turning things into functions and removing characters wasn’t enough to solve the problem.
This gets a little technical, but there are certain ways of writing code that work better when compressed with zlib. I had to optimize the code with that in mind, which took quite a bit of effort.
In the end, I didn’t want to remove features that were already in the game before submission, so I had to make the decision to remove the score submission feature.
Instead, I was able to implement the achievement system in the Wavedash version.
The final size came out to 13,308 bytes, leaving just 4 bytes of space.
Making a game within a 13KB limit was already challenging enough, but I didn’t expect to be fighting with the file size right up until the very end.
Final Thoughts
If participating in js13kGames helps even a little with getting more people to discover my games and Flyable Heart, then I think that alone makes it worthwhile.
If you’re interested, please give the game a try!
And if you do, I’d love to hear what you think. Feel free to share your thoughts with me on X or elsewhere!