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Earlier this week, the news broke that the long-awaited ROM hack Super Mario Kart Deluxe finally has a release date: December 25th, 2026.
The ambitious project, led by MrL314 and ScouB, has been on Time Extension's radar since the site began in 2022, and looks to be one of the most impressive hacks ever released for the classic Super Nintendo kart racer, introducing new characters, modes, items, and so much more. Even better, none of these additions are reported to overwrite any base-game content, so you can still enjoy the original Mario Kart as is, alongside all this new content (provided you have a legal copy of the ROM on hand). It's also said to work on real hardware too, in addition to emulators, with the project shaping up to be something truly special for the retro Mario Kart community.
In the past, I've chatted briefly with MrL314 about Super Mario Kart Deluxe, but with the finish line now in sight, I felt it was time for a more in-depth discussion about the history of the ROM hack and what's in store for players. During this conversation, they told us more about how they joined forces with ScouB in the first place, the strange discoveries they've made, the challenges of introducing new characters, and a ton of other details, alongside sharing some exclusive images of the hack in action. So, if you're just as excited as we are, you should read on to find out more:
Time Extension: First off, where did the idea for SMKDX come from? When did the project originally start?
MrL314: One of my favourite facts to share is that Deluxe didn't originally start as one mod; it actually started as two. Mario Kart Deluxe, from my side of the project at least, was something I'd had in mind for years: to expand Super Mario Kart's capabilities and push the engine to its absolute limits. I had my own project where I added new battle modes to the game and restored one of the prototype battle modes that eventually got cut from Super Mario Kart: the Gate Race.
At the same time I was working on that mod, ScouB was working on his own project, putting prototype tracks back into Super Mario Kart. That project is where the name Super Mario Kart Deluxe comes from. He had been asking me for help programming systems for his hack, and then what happened was we started talking a little bit more one-on-one about the projects and, at some point, he asked, 'Would you like to be more involved with my project for Deluxe?' He was planning things like making more track themes, adding more characters, and boosting the CC to 300, which I thought was hilarious. So I was like, 'Absolutely, I want to be a part of this. This sounds like fun.' That was, I think, sometime in December of 2021.
Since then, we've basically covered each other's bases. He's very good with graphic design, artwork, and everything, and I'm pretty lacking in that department. But I have a lot of programming knowledge, so I help develop the little ideas we both have.
Time Extension: When I spoke to you back in 2022, you mentioned that, besides creating “a deluxe version of Mario Kart”, another goal of the project was to learn more about how Mario Kart was made. What have been some of the more interesting discoveries you’ve found?
MrL314: There are quite a few very small weird things we've come across. One of my favourites is the discovery that during Grand Prix, the camera isn't actually set properly; it's a degree off. It's very, very weird, and it does not affect gameplay at all. But we had to fix it because it caused issues in mission mode; we have a mission where you have to aim very precisely at something, and that one degree affected how people aimed.
Also, this is very speculative, but we also found what we assume to be a last-chance life system. So when you had a game over, a roulette would spin one last time, and it would have an unused 1-up come in and give you an extra life. That got scrapped; I don't know how early in development, but little pieces of that code are still there.
There are also the differences between PAL and NTSC. For a while, we knew that there were differences with things like speed and range for throwing and everything, but we got to concretely write down exactly what the differences were while we were working on adapting Deluxe over to PAL.
Another one of my favourite weird little quirks is that the player racer, the way it's displayed, is completely different from the rest of the game. I'm trying to think of a way that I can explain this that's not super technical. Have you heard of the thing in Donkey Kong Country Returns where the players aren't actually 3D; they're 2D renders that are placed in the world? It's that sort of thing.
Obviously, nothing in Super Mario Kart is really 3D. I know that's going to anger a lot of people. There's nothing that's actually rendered in 3D, but there are certain ways that the DSP is able to calculate how far something is from the screen, the size that it should be relative to what you're zooming in on, stuff like that. But because the player is always in a specific spot on the screen, they don't actually need to do those calculations. Instead, what they do is basically just render the player statically in front of the screen. And that pretty much never changes. They just manually adjust where the player's height is based on how high they jump. So they're not actually existing in the 3D world whenever they're on the screen. That was really fun to learn about. That also became an issue when I was working on my little side project: Resident Evil Kart, where I had to override that system to make the player render in 3D space.
Time Extension: I think I remember hearing about this project.
MrL314: So that one spawned because of Deluxe. We were making a mission where we were messing with the cameras to either put them in front of you or to the side to mess with how you're controlling, because there were missions in Mario Kart DS like that. It was very cathartic to make that. It was never a very serious thing, but I took creating it very seriously. I ended up making my own tools to render the camera in my little editor so I could make sure the camera looked right when I placed them. That was honestly a very, very fun project, and it was a very good way to take my mind out of Deluxe and then bring it back with some fresher ideas to keep continuing.
Time Extension: One of the new additions to SMKDX is the new characters (such as Wario, Daisy, Bowser Jr., Kamek, Waluigi, Birdo, Dixie Kong, and Toadette). It’s an interesting selection. What went into deciding who made the cut? Could you talk a little bit about the challenges of adding these into the game?
MrL314: So, this is something that always gets brought up: the character selection. It's really funny. ScouB pretty much decided the character roster when it was his original project, but we did talk about which characters would be feasible to put into the game. One of the considerations we had was technical, but there was also more of a social aspect to it, which is... how do I put this lightly? The original game is very much an adult man's roster.
Of course, there are some options to pick if you're a woman or a child, but we wanted to give a few more choices than Peach or Yoshi, which I see a lot of women and kids default to when playing Super Mario Kart. We had a lot of technical restrictions, though.
So the way that Super Mario Kart works is that there are four palettes that are reserved specifically for the characters. And in the original game, this isn't a problem because each pair of characters shares a palette. So, for example, Mario and Toad share a palette. So, in the original game, they can have the eight characters use those four palettes, and that's all the space that they need. They then use the rest of the palette for things like items, obstacles, and then the track itself, of course.
When we're adding our characters, though, we also need to make those same considerations, and it got a little bit complicated because we do have two characters in particular that use unique palettes, which are Daisy and Waluigi. So, that causes really big problems because if you have two characters that have a unique palette, and then you have three pairs of characters that have different palettes, you have five palettes, and you can't do that in a race. So we had to develop a system to help select the other racers for Grand Prix, specifically, so you could have eight racers on the track. So what we actually do is, whenever players pick their initial selections, we check which groups of characters can be selected, and then we randomly pick characters from that group to make sure the number of palettes isn't too big to fit in a race.
Time Extension: Has it been simple changing the UI to have these new characters selectable? Or are there any hidden challenges there as well?
MrL314: In some ways, yes; in other ways, absolutely not. So sometimes, sometimes during game development, you have things that absolutely blindside you by either how simple or how stupidly complex they are. So one of those that hit into the stupidly complex category is the title screen.
We had to figure out a system to be able to swap between all of those palettes live to have our own little animation on the title screen with the different characters. Then for the character selection or the cart selection menu, because we have all of the characters on screen, we have to have all of their palettes loaded, and that became a little bit of an issue because the game didn't really have much leeway in terms of the palette space. So we had to be a little bit clever about how the palette management would be working for certain parts.
Another thing that was actually very interesting was the podium screen. So each of the characters has special, specific sprites for their podium animation for the bottom half of their character, because obviously their bottom half isn't ever shown during a race. So, those were a lot more complicated than we expected, but there were things that were a lot easier than we expected, like the little animation for the faces whenever a player finishes the race was actually pretty smooth.
Time Extension: Besides new characters, your feature list also mentions a campaign mode with custom bosses. How exactly will this work? Will this be similar to Mario Kart DS & Mario Kart Wii (in other words, a mix of battle arenas and races)?
MrL314: The basic premise is that it's pretty much like Mario Kart DS. That was my big inspiration for it. So you have these worlds that are split into groups of nine missions: eight missions and then a boss.
Each of these is intended to teach you how to play the game and to refine your skills. So there will be missions like exploring while collecting coins to enter parts of the track you didn't even know existed, or learning how to aim or use items properly. As for the bosses, they're partially me just wanting to show off a little bit, just to be like, 'Yeah, we can do crazy things with the SNES. So, why not just have a little fun with it?' But they're, again, also there to test your skills, too.
We do have some that are races, some that are battle-specific, and some that are specific to a mode that we call battle race, where you have both a life system and a lap system. We have all of these elements mashed together to make what is, in essence, a practice mode. So that you can go there and hone your skills and learn how to play better, and you can check the rankings to see how you are doing. It's definitely not something that we intend for players to try to take on in one sitting. It's a very hard mode. The original game is hard, and we didn't want to take that edge off too much. So, we still have that level of challenge. And, of course, there are rewards for completing different parts of mission mode. So there's a little bit of incentive for players to want to try to refine their skills.
Time Extension: You also mention new items. Are these based on things we’ve seen from previous Mario Kart games, or are there any new additions we should be looking out for?
MrL314: It's a little bit of a mix of both. The first thing that we wanted to do was to fulfil the dream of every Super Mario Kart player, which is to use the CPU items. We all wanted to use the egg and fireball. So our first goal was to be able to have players use the existing items in Super Mario Kart that you can't use; the blue shell was also my insistence. I remember a while back I posted a little fun thing, like, 'Hey, I put a blue shell in Mario Kart,' and it got absolutely heated. I was like, 'Okay, yeah, I know I'm doing this right.'
We also wanted to include the multi items from the rest of the series, like the triple green shells, the triple reds, stuff like that. But we ran into real limitations in both the hardware and play styles. In the Grand Prix, you can only have two field items, which appear physically on the map at one time. So, of course, we can't have triple items because one would always get overwritten. So we decided to do doubles instead, and that worked perfectly. Doubles felt balanced, and they also weren't de facto just better than single items. It was just, "Hey, you have two of them now, so be strategic with how you use them." There are also some other items returning from other entries in the series. These include: the Super Leaf, or the Tanooki Leaf, the Blooper, the Bob-Omb, the Boomerang Flower, and the POW Block
Then there are the two original items:
- The P-Balloon - An homage to Super Mario World. Similar to the feather. In some ways, it's better because you can cover more distance with it, but worse because it's much slower and you don't have direct control while you're in the air.
- Yellow Shell - One of my favourite items. Another callback to Super Mario World. In Super Mario World, all four different shells give Yoshi different abilities. When Yoshi has the yellow shell, he can jump in the air, and then when he hits the ground, it causes an earthquake, and everything shakes. We wanted to have that feeling of a very powerful object. So the yellow shell is fast, it's explosive, and it's invincible. It fires like a bullet, straight forward, and it will plough through all the races and the items in its way.
Time Extension: In terms of the new cups, is it the same (a mix of ideas from past games and new tracks)?
MrL314: Every track theme that's added is loosely a parallel to a theme in the base game. For example, we have Daisy Garden as our equivalent to Mario Circuit. And Daisy Garden is based on Daisy Circuit from Mario Kart Wii and Peach Gardens from Mario Kart DS. That's something that applies to all the tracks. Here's a list of the others:
Desert Land - Our Donut Plains. It's based on Dry Dry Desert from the different Kart games and also Super Mario Bros. 3, which is why we have the Angry Sun. I love the Angry Sun! I know it makes people mad, but it's fun; I like it. Just give it a chance.
Hazy Cavern - Our Ghost Valley, which is inspired by Hazy Maze Cave from Super Mario 64. It comes with my favourite character in the entire game: Dorrie. Everybody on the team loves Dorrie. And it also has the gimmick of the falling rocks from Hazy Maze Cave.
Fiery Volcano - Our Bowser Castle, which is kind of a mishmash of the Mario Kart Super Circuit Bowser Castle and Grumble Volcano from Mario Kart Wii. As the race progresses, the track actually does change, and parts of the track sink into the lava; I'm very proud of that feature. It was really, really cool to get that to work on the SNES.
Wario Rally - Our equivalent of Choco Island. It's a direct reference to Wario Stadium from Mario Kart 64, complete with a bunch of Wario faces plastered around the track's perimeter. But it also has a gimmick where there are speed panels that can be on or off based on the time. So there may be a short path and then a long path, but the long path could have a speed panel on it, so it could actually take you less time to go on the long path if you time it right.
Stormy Jungle - Our Koopa Beach, and in my opinion, one of the most beautiful tracks. I love what ScouB did with the aesthetics. That's not based on any track in the series. Originally, we wanted it to be so that we could have the rain effect from Donkey Kong Country constantly on during the level, but that was way too much of a technical challenge to get to look and feel right. It would also have meant removing the rank position display during the race, which we didn't really want to do.
To make up for that, we have it so that everything on the track looks like it's being rained on. So there are tile animations that look like little raindrops in the puddles, and the background is raining; then, on the last lap, like in Donkey Kong Country, the rain clears, and it becomes all sunshine. So we fade the palettes to something that's sunnier, the rain animations stop, and you get a completely different scene. The gimmick is also inspired by the Super Circuit track Sunset Wilds, where it changes from night to day.
Poison Swamp - Our "Vanilla Lake", though it's a very big stretch to call it that. It's more like a harder Donut Plains. It has little wild Goombas waltzing around while the race is underway, which was a really fun mechanic to do because we had to be very strategic about how we place the Goombas because we can only realistically have four on the track. Otherwise, they would always end up spawning in the same place because of how the Super Mario Kart engine works in the backend.
Star Road - I almost neglected to mention this. So this is our Rainbow Road, based on the Star Road from Super Mario World.
Time Extension: I’ve also seen that you’re introducing various multiplayer modes (plus additional CCs, Mirror Mode, and music). At this point, I have to ask: what have been some of the biggest challenges with expanding the game in this way? Has it been difficult to ensure it still runs correctly on original hardware?
MrL314: A lot of this is just from years and years of experience working with this hardware. There are certain things you just know for a fact you can't do with either the engine or the specific hardware itself.
One of the big challenges we had was that we wanted it so you could play the entirety of Super Mario Kart in Deluxe. We wanted the original game to be fully intact. But that also led us to have an interesting kind of limitation. When we were implementing things, we'd have to do them as the original developers wanted. For example, when we added new items, we had to piggyback on their existing system to make those work. In some cases, that was easier. And in some cases, that was a very hard thing to do, especially when it came to bosses.
Bosses were a big pain because if a boss is using an item, you don't want players overwriting it just by using the same item. I ended up implementing a new system called extended items to fix that. Extended items are items that are specifically not for being used by the player. So a boss could use them, and they won't be overwritten like in the base game. But the one thing that always stumped us with adding stuff like this — this is one of the sad truths about game development in general — is that complexity isn't linear. Adding one new thing to a game doesn't make it a little more complex; it makes it a thousand times more complex.
Like, take, for example, the Bob-omb; you start with a simple question: 'How many times should a Bob-omb damage a player?' It should be something like one, right? That's pretty obvious. But what if a player runs into it? That should still be one. But the engine doesn't necessarily make that an easy thing to do. You have to kind of hack around that system so the Bob-omb hit is treated differently from an explosion, because that system can override other interactions. You then have to think about what happens if the player is invincible. Or what if there's a second bomb in the explosion? If that explodes, do the players get hit once or twice?
There are so many little things that come from just one simple idea of 'I want a thing that explodes in the track.'
Time Extension: Beyond ScouB and yourself, who else is involved in this project?
MrL314: Yeah, so the team is actually a lot bigger than people would actually imagine. We also have Icesan, a programmer we brought in to help optimise code and reduce lag, and Ramon. Ramon created some of the tools that we use for converting our tracks from Stifu's Epic Edit into being compatible with our build system. He also created some of the tools for helping us with having our sprite layouts for the characters in max size and then shrinking them down to smaller sizes so we could just do the touch-ups on those. Doing that by hand is a pain in the butt.
There's also Dirtbag, who created the tool we used for the title screen demos and was also very helpful in testing my initial build system for the entire project, as well as Cajarito, who is our box artist and character artist. They did a phenomenal job on the box art (which we showed in the recent teaser), and the individual character artwork you'll see in the manuals when the hack is released. Then we have some musicians: Pinci, Random, and VVonk.
Pinci and Random are our two main composers, and VVonk is creating a secret special song for the game, which I won't talk about here. There's also our trailer consultant, Kert Gartner, and our website designer, the_drunk_strawberry. The website will be our project hub and a place to submit records. It's not live yet; we plan to launch it with the project itself. We also have playtesters too, whom we are keeping anonymous for now, specifically because we don't want them pestered by people asking questions about the game. We'll thank them publicly when the game comes out.
Time Extension: Finally, you’ve set a tentative release date for Christmas. What’s left to do on the project before then? Does the team have any plans beyond that?
MrL314: As for what's left to do, basically everything functional about the game is completed, and it has been for a couple weeks. But we're going over doing final polishing on all the features, making sure that there's nothing game-critical that's still breaking. We're fixing some very stubborn bugs that have bothered us the entire project — I have two in particular that are very annoying. We're still polishing some of the final songs; we're working on the release trailer and the website, and finalising the manual and the box designs.
As for plans beyond that? For me, I don't know; probably take a nap. I love this project, but it has been so tiring.
Once we finally finish the hack and release it, we want it to feel like how games were released in the 90s. Once it is out, it's out. Obviously, if there's something that's extremely crucial that we missed with the game that is game-breaking, like, 'Oh, somebody can't select this player and play the game', then of course we'll fix those bugs, and we'll release a small patch later. But if nothing major goes wrong, then basically, what we release is what's out. We don't want this to be a forever project.