Interview: Developer Gridattack on Super Mario Kart Horizons

Super Mario Kart Horizons is one of the most ambitious ROM hacks in recent years, reimagining the classic SNES racer with twenty brand new tracks, four custom battle maps, an original soundtrack, and presentation elements like a custom manual and box art. The project, available at RomHacking.net and RomHackPlaza, represents the culmination of over a decade of tinkering, iteration, and dedication from its creator, Gridattack. Horizons has also been the subject of an in-depth review and longplay on Retro Replay.

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In this interview, we sat down with Gridattack to discuss the inspiration behind Horizons, the development process, the challenges of hacking a game as technical as Super Mario Kart, and the reception from the community.

Interview with Gridattack (10.02.2025)

Retro Replay: What first inspired you to start romhacking, and how did you discover the scene?
Gridattack: I’ve been into games since I was a kid; Super Mario Bros. 3 was the first game I ever played. Back in school, I’d draw custom Mario Kart tracks in a notebook I still have today. At home, we had a modest Windows XP PC, and one day my dad installed a NES emulator with a few games like Contra and Punch-Out!! That got me curious about SNES games, and I eventually found ZSNES and discovered Super Mario World. I wanted more 2D Mario content and came across Mario Forever, which inspired me to make my own levels. After some googling, I found out Super Mario World could be edited. I joined SMW Central, downloaded Lunar Magic, and started experimenting; though I never posted my work, since I was nervous about being a newbie. From there, I discovered sites like Zophar’s Domain and realized just how many games could be modded.

Retro Replay: Do you remember your very first hack, whether big or small, and what lessons it taught you?
Gridattack: I see I could reply to this question in 2 ways: When I first modded a game, and an actual released hack.

Gridattack: Following up the previous question, modding SMW taught me to just have fun and try to come up with ideas that the base game didn’t present to you, but was technically possible. Since I didn’t post on the forum it also taught me to be resourceful in trying to find how to do X or Y stuff, or read up the forum for any information that might be relevant. Regarding an actual hack, NSMB Deluxe! it taught me to not give any precise release date! I remember failing to meet the date I gave at first, due to gathering some attention. Since I wanted to give the best impression, when releasing NSMB Deluxe! I had to learn how to use a video editor software, as well as other stuff needed to properly make a good impression and release.

Retro Replay: What drew you specifically to Super Mario Kart as the foundation for Horizons?
Gridattack: Since SMK is so easy to mod, thanks to Epic Edit, and me having a notebook of track ideas, I knew I could whip up something. I did play around with custom SMK tracks and did want to release a full custom track, as back then there weren’t many mods, due to the limitation of not being able to edit the CPUs paths.

Gridattack: Making a custom SMK track is really easy, I feel its kinda like painting pixel art; so I decided to stuck with it. I did try to make a custom MKW track but was never able to import my custom models in it, and actually testing custom SMK content is much faster.

Retro Replay: Horizons released in 2024, but your work on New Super Mario Bros. Deluxe! dates back over a decade. How did your approach evolve between those projects?
Gridattack: NSMB Deluxe! wasn’t really playtested; I didn’t get any feedback and thus the hack has many downfalls in the custom sub-areas department. With Horizons I made sure to test beforehand.

Gridattack: Regarding making content, it was just making the custom levels & tracks as the mood allowed. I also did have experience in between as I did make all the custom tracks in Sour Music Kart, helped with testing and graphics there and helped DirtBag playtest Super Baldy Kart, so I was much more versed in how to approach a project like Horizons.

Retro Replay: Was there a particular Mario Kart game in the series that influenced your vision for Horizons more than others?
Gridattack: Mario Kart: Super Circuit! is my favorite in the series; I guess some of the difficult content from that game kinda crept in some aspects in Horizons in terms of track design.

Development Process

Retro Replay: How long did Horizons take from the first idea to its 1.0 release?
Gridattack: This one is difficult to measure, but I started dabbling around in modding SMK with an editor named TrackDes. You couldn’t edit the CPUs path so it was mostly a single player and to myself thing.

Gridattack: Once Epic Edit came out and you could edit the CPUs pathing, I made some videos and uploaded them to youtube. Since it was now possible to provide an actual racing experience with the base game, I decided to fully commit into making a full SMK hack.

Gridattack: I uploaded some videos starting in mid 2010 in which ou can see initial versions of some of the tracks, so you could say it took around 14 years, but it was really on and off, there were some years of inactivity to my hack and inside this time period I helped make Sour Music Kart, which took a couple of years as well to make.

Retro Replay: What was the single hardest technical challenge you faced during Horizons’ development?
Gridattack: Honestly, you could say things like programming the custom music, extending the base capabilities of the base game such as the extra modes and different palette per level, but I didn’t make the code for those, so they don’t count.

Gridattack: However I can tell you that the thing I remember the most was moving the pillar/icicle object from the Ghost Valley/Frigid Mine, due to the editor not supporting it, I had to do it via hex editor and map out beforehand where I wanted for the pillars/icicles to appear. It was really time consuming.

Gridattack: The other difficult aspect was playing around with the limitations of the base game, such as the colors per tileset, the backgrounds, etc. Figuring out how to best optimize stuff felt like a puzzle, and I really enjoyed finding solutions. Particularly porting the mountains you see in Alpine Pass was challenging and required precise planning and thinking on where each tileset and color palette needed to be.

Retro Replay: Did you work solo on Horizons, or were there collaborators that helped with music, sprites, or testing?
Gridattack: Horizons had multiple people collaborating directly and indirectly: The biggest influence is Cocatriz; he is the best Spanish player at the game and he has his own cool SMK hack that is challenging (SMK 20XX). Without him ever telling me that the courses needed to be driveable with the heavy weight characters and his pro player feedback in making the courses more fun for the pro playerbase, Horizons wouldn’t have that wide appeal. The second most important influence is DJ Grisned itself. He took the mantle in learning how to use PrixCompose, a tool to make SMK music, and he also helped in making custom sprites, including all the drivers and the items. He also helped in making the menu, driver select and podium screen, as I really was at a point where I knew how to do it but couldn’t be bothered to do it due to laziness, so I really thank him for picking up the slack. Ice3 provided the custom code for implementing Mirror Mode and it being unlocked, as well as technical debugging and questions I had about the game, due to their immense knowledge in how the game works. R4M0N made the custom code that allowed for each track to have its own custom palette; thanks for listening to my ramblings and ideas and making them possible! MR. L314 provided custom code to tweak some behaviors and answers to particular sections in the hack, to make sure the hack is as polished as it could be. ScouB was also of great help as he also knows the game code inside out, and provided references on where to look in the code to achieve a particular thing. Lafungo, a top player across the world, helped me in testing the hack for any potential breaking shortcuts as well as providing insightful feedback from a competitive player standpoint.

Gridattack: There are other members in the community such as DirtBag, Stifu and other members in the SMK Community & IRL friends that helped me in being able to complete the hack.

Retro Replay: The new soundtrack in Horizons is one of its highlights. Can you talk about the process of putting that together?
Gridattack: Initially, I was considering using MS-1 music patches, but DJ Grisner reached out in the mid-2020s to offer custom compositions. I had learned from past projects not to pass up help, so we collaborated. I provided references and mood direction, and Grisner brought them to life. The first track we tackled was Sunrise Ridge, heavily inspired by Celeste’s final level. From there, we developed tracks one by one; sometimes using game references like Super Monkey Ball, Kid Nikki 3, Eschatos, Rosenkreuzstilette & Frogger PS1 to guide the tone. Some songs, like Rice Terrace and the battle theme, came together quickly. Others, like Rainbow Road and Frigid Mines, were more challenging and required several iterations, as well a bit of creative tension in how the soundtrack should be approached: if it was similar to the base game or something new. Naming the soundtrack was fun as well; I asked DJ Grisner if they were fine with it by not using the theme’s name and me naming the soundtrack despite not being the creator and they agreed. Tried to sound a bit silly and memorable for each one and set a playful tone as well.

Retro Replay: For NSMB Deluxe!, you recreated SMB1 and The Lost Levels. How difficult was it to balance faithfulness to the originals with the style of the DS game?
Gridattack: The biggest challenge was the game not having the same behavior as some of the obstacles you see in the originals. The infamous “flying fish” come to mind, as the base game has them but you need water to be across the entire level for them to work or the wind from The Lost Levels being absent, which required shortening some levels.

Retro Replay: Did you ever feel like scrapping Horizons during development, or was your vision clear from the start?
Gridattack: Development evolved over time. Initially, I just wanted to make a high-quality hack since most existing ones were lacking. I knew custom graphics would be key in achieving a better impression. There was one rough patch when DJ Grisner took a break, and progress stalled. I even considered donating the track designs to ScouB’s SMK Deluxe project. But he reminded me Horizons had its own identity, and I’m thankful he helped me stay on course.

Retro Replay: Why did you decide to make a custom Manual, Cart Label and Box?
Gridattack: At the time, I had a medical issue that kept me bedridden, and my main tools were on a desktop PC I couldn’t use. I only had my Macbook, so I shifted focus to the game’s presentation. I noticed ROM hacks were being bootlegged and sold on sites like Etsy, often with poor-quality cover art. To prevent that, I created official artwork, a box, and a label. So if it was going to be sold unofficially, at least it would look good. The artwork was commissioned from my dear friend Laurie.ink, and I adapted it for the box and label. The manual was more of a spontaneous “why not” decision, and it takes heavy inspiration from the original SMK manual.

Design and Gameplay Choices

Retro Replay: Why did you decide to create wide tracks with plenty of room to maneuver in Horizons instead of sticking closer to the tighter original layouts?
Gridattack: Actually the original track layouts are generous in this category for the most part. The top priority was to make the hack being able to be driven at max speed on 150cc with Bowser or DK Jr. This is also a critique to those hacks that have serpentine and very narrow track design, which are impossible to drive at an appropriate speed with the aforementioned characters, as most people just play as Koopa Troopa or Toad.

Retro Replay: Horizons includes Mirror Mode and a hidden Hard Mode. What made you want to include unlockable content?
Gridattack: Due to the advancements in modding the game, adding entirely custom content is easier now. I kinda wanted to include mirror mode as it has been demonstrated that it can be done beforehand. Ice3 was generous enough to make a custom unlockable version of their mirror mode and suit it to my needs. Hard mode was a bonus for people who really wanted a challenge and for pro players.

Retro Replay: In NSMB Deluxe!, you added new areas for Star Coins. Was it important to you that exploration had as much weight as pure platforming?
Gridattack: Since the original levels are short, I used these opportunities for the most part to make levels that use the capabilities of the NSMB engine. Some of the larger custom areas were in part due to the demand at that time of hidden and big areas to explore, but in retrospect these custom areas more than less feel out of place.

Retro Replay: Horizons features 20 new courses and 4 new battle maps. Do you have a personal favorite among them?
Gridattack: This one is hard to answer, so I’ll answer one for each category: Battle Map: Battle Map 4, the rainbow road one. Me and my friend Gustavo always spent the most time playing this battle map. Race Course: Frigid Mine 2; this was originally a track I created for Sour Music Kart, but with the changes & additions in the tileset and themes is really a great track to drive.

Retro Replay: How did you decide on the themes for Horizons, like grassy plains, abandoned mines, and jungle ruins?
Gridattack: I wanted to mix familiar Mario themes with fresh twists. Some themes, like Jungle Ruins, came from my experience beta-testing Newer Super Mario Bros. Wii. Others, like Sparkle Oasis or Rice Terrace, were inspired by classic Mario elements like SMB3 or SML: Chai Kingdom. I often blended existing ideas; like combining Donut Plains with Bowser Castle; to create something new. I was also influenced by the more realistic look of Mario Golf: Toadstool Tour, which inspired tracks like Alpine Pass and Sunrise Ridge. In fact, Sunrise Ridge is a small tribute to Celeste, which really resonated with me at the time. Frigid Mines was the hardest theme to build around, as mixing Ghost Valley with Vanilla Lake left little in options, but I’m happy with the results.

Retro Replay: You’ve updated sprites and presentations in both of your major hacks. Do you think visuals are just as important as mechanics in a romhack?
Gridattack: Yes. One of the biggest issues I have and the SMK hacking scene suffers is lack of original or poor content. Most of the hacks don’t change the themes or palettes, and due to the game being easy to mod, there are many track only hacks that dilute the quality.

Gridattack: If you want to stand out, having custom themes and/or colors is a must, along with new tracks. This helps to differentiate the hack from others, as few hacks are able to create custom themes.

Retro Replay: Was there ever a course or level idea that didn’t make the cut because it just didn’t work in practice?
Gridattack: You could count the tracks that don’t bear any resemblance to the final ones from my old youtube videos, but these were more tech demos and me having fun without intending to make a full hack.

Gridattack: However when I was in the process of making Horizons, I scrapped a Jungle Ruins track, which you can see here. I just wasn’t feeling it and the track was too narrow on the broken section in the poisoned water, but looking back at it, it had potential. Maybe for a later rerelease or something it’ll see the light of the day.

Gridattack: There was also the Frigid Mine Battle track, which didn’t really work in practice, despite trying to follow the original template of Battle Map 4 of the original game by providing different obstacles in the narrow sections.

Community and Feedback

Retro Replay: How has the reception to Horizons compared to your expectations?
Gridattack: The reception surpassed my expectations! Definitely appreciate every one that makes a video showcasing or playing the hack. While it’s impossible to please everyone, the vast majority of the reception is positive, and I’m glad people are enjoying my hack, which is for the fans, by the fans.

Retro Replay: Did community feedback during testing shape Horizons in meaningful ways?
Gridattack: Yes. The Super Mario Kart community, which makes the yearly big tournaments in Europe, ran a beta version of my hack a couple of times after the main tournament had ended. I was able to gather feedback from the pro players as well as see other people playing the game and take notes.

Gridattack: I’m really grateful for the opportunity given and for the feedback provided.

Retro Replay: What advice would you give to someone who wants to create their first romhack today?
Gridattack: I would suggest just trying it! It also depends on the game and what you want to do, but the most important part is that you have fun!

Future Projects

Retro Replay: Do you have plans for updates to Horizons beyond version 1.3, or do you consider it complete?
Gridattack: I consider it complete. I would only update it if I find a game breaking bug or something. I would like to update the music volume to be a bit higher, but unfortunately DJ Grisner left the scene and I have no idea how.

Retro Replay: Is there another franchise you’d love to hack besides Mario?
Gridattack: I’d love to make some custom levels for the Super Monkey Ball games on the gamecube.

Retro Replay: Would you ever consider working on a collaborative hack with other big names in the community?
Gridattack: Yes. Unfortunately I don’t have much free time these days, but I’m collaborating today with Cocatriz in his SMK 20XX hack to create custom themes to elevate the presentation of his project.

Retro Replay: Do you see romhacking as a hobby that feeds into game development skills, or as its own standalone art form?
Gridattack: There is something to learn in ROM Hacking that can feed into game development skills, particularly the game designer portion of it, since you create custom levels and ideas and it pushes you to see how you can execute them.

Wildcard / Fun Questions

Retro Replay: If Mario Kart Horizons had a guest character from outside the Mario universe, who would you put behind the wheel?
Gridattack: I would LOVE to add Sutte Hakkun from the series of the same name; it’s a really great puzzle platformer on the SNES which is on the Nintendo Switch Online to play as well!

Retro Replay: Which course in Horizons would you least want to drive on in real life?
Gridattack: Got a couple in mind: Alpine Pass 3, Evening Isles 1, Rice Terrace 2 and Sunrise Ridge 1.

Retro Replay: If you could time travel back to 1992, would you pitch Horizons directly to Nintendo?
Gridattack: Not really; you know how Nintendo is against unofficial modifications haha, so rather not risk it! I’m just curious if anyone from the original dev team has seen any SMK mod and what they think of it.

Retro Replay: What’s your go-to Mario Kart character when you’re not busy testing your own tracks?
Gridattack: I used to play Koopa Troopa, but when I switched to Bowser to play test I just sorta got used to him due to the amount of time spent, so I always choose him.

Retro Replay: Imagine you’re in a Mario Kart race yourself… what’s the one item you’d want guaranteed in your inventory?
Gridattack: A Boo; really great defensive and offensive item.

A huge thank you to Gridattack for taking the time to share the story behind Super Mario Kart Horizons. Please visit his YT channel, here for more updates. The project stands as both a love letter to the SNES classic and a showcase of how far ROM hacking has come. Players can download the hack at RomHacking.net or RomHackPlaza.

If you enjoyed this feature, you may also like some of our other developer interviews on Retro Replay, including Gabbi on Earthbound Beginnings, PacnSac Games on Mr Gimmick 2, Letstalkgames with xmangravyx, and Southbird on Super Mario Bros 3Mix.