Undertale/Deltarune NSFW mods?

[losstie27]

Given the release of Deltarune Chapters 3&4 in just a little over a month, now seems like the best time to ask: "Why hasn't anyone made a nude sprite edit mod for either Deltarune or Undertale yet?" The games seem to be relatively easy to mod, with dedicated mod tools existing, and decently good documentation. The characters themselves are immensely popular when it comes to being lewded, so much so, that even a quick Rule34 search gives over a hundred edited spritesheets for just Deltarune alone. Below are just some of the immediate favorites I could find for inspiration. I, personally, think this is an untapped market.
 

Spoiler

 

[shootingstarCR]

Seconded, really want to see Deltarune NSFW mods

[Guest]

Same here

[Catnatic]

It is relatively easy to mod with UndertaleModTool which allows replacing sprites for most games running on GameMaker, so it's a wonder why there hasn't been a dedicated group of furries that modded the game to have nude sprites by now.

[GooseVis29]

The only "NSFW Undertale mod" I've found is SexTale, it only has Toriel sprites
https://gamebanana.com/mods/587652

Edited April 22, 2025 by GooseVis29

[losstie27]

5 hours ago, GooseVis29 said:

The only "NSFW Undertale mod" I've found is SexTale, it only has Toriel sprites
https://gamebanana.com/mods/587652

I hadn't seen this yet. That's cool. Though the sprites in the photos are kind of hilariously exaggerated.

 

8 hours ago, Catnatic said:

It is relatively easy to mod with UndertaleModTool which allows replacing sprites for most games running on GameMaker, so it's a wonder why there hasn't been a dedicated group of furries that modded the game to have nude sprites by now.

 

I feel like the game lends itself fairly well to a nude mod too, with how text-heavy it is. Something similar to your nudity reactions mods for the Pokemon games could work perfectly here I think. The story scenarios there could be really fun to mess around with I think.

 

[losstie27]

 

I do not remotely have the time nor willpower to take on fully respriting even one character, but here are some concepts I made for what a nude Ralsei could look like. I'm not willing to let go of this idea, I love it so much. That said, I'd be more than willing to help anyone who takes on the task, like with NPC characters and such.

Edited April 23, 2025 by losstie27

[msrio]

On 4/23/2025 at 5:42 PM, losstie27 said:

 

I do not remotely have the time nor willpower to take on fully respriting even one character, but here are some concepts I made for what a nude Ralsei could look like. I'm not willing to let go of this idea, I love it so much. That said, I'd be more than willing to help anyone who takes on the task, like with NPC characters and such.

I like the idea of an nsfw mod for this game, I might edit some sprites

[losstie27]

7 hours ago, msrio said:

I like the idea of an nsfw mod for this game, I might edit some sprites

 

I'd love to see that if you did. With how big of an undertaking a mod like this would be, maybe the best course of action would be to run it like Viewier's Platinude, and take sprite donations from people to compile into a larger mod. It's not ideal, but I guess we'll have to see.

We'd probably need a good selection of sprites anyways before doing any story edits, which is what I'm most interested in. You guys should all totally share any lewd story changes you have in mind though, to help keep the thread alive.

[losstie27]

Chapters 3 and 4 come out in just under a month now and there's still unfortunately no progress towards a mod. Really hope the right person will see this. Here's another sprite edit I found

 

 

 

 

[losstie27]

On 4/23/2025 at 6:42 PM, losstie27 said:

 

I do not remotely have the time nor willpower to take on fully respriting even one character, but here are some concepts I made for what a nude Ralsei could look like. I'm not willing to let go of this idea, I love it so much. That said, I'd be more than willing to help anyone who takes on the task, like with NPC characters and such.

Deltarune releases in just 10 days. Here's another concept I made for what this hypothetical mod could look like. Let me know what you guys think!

 

[losstie27]

On 4/22/2025 at 1:06 AM, GooseVis29 said:

The only "NSFW Undertale mod" I've found is SexTale, it only has Toriel sprites
https://gamebanana.com/mods/587652

 

I'd also like to add, since this thread is for both Undertale and Deltarune, that this mod was updated a few days ago to include anthroified versions of most of the Ruins monsters. It's not really my tastes, but maybe someone enjoys it.

[Buddussy]

Will be replying here to bump the thread and keep an eye on it in case developments arise, sprite porn modding is such an underappreciated and underrated niche.

[Buddussy]

On 5/25/2025 at 12:04 AM, losstie27 said:

Deltarune releases in just 10 days. Here's another concept I made for what this hypothetical mod could look like. Let me know what you guys think!

 

I like this one.

 

A great source of inspo would be animations from Mayin and SuicidalPixel, since they've both done a bunch of Deltarune/Undertale content.

[losstie27]

10 hours ago, Buddussy said:

Will be replying here to bump the thread and keep an eye on it in case developments arise, sprite porn modding is such an underappreciated and underrated niche.

 

I more than agree. Sprite nude mods nearly always look better to me than 3D models.

I will say, without spoiling chapters 3&4, Deltarune would be an absolutely massive undertaking to nude mod with the drastic increase in content we just got. Starting smaller with just a nude Kris or Ralsei hack would be much more feasible I think. 

[Buddussy]

10 hours ago, losstie27 said:

 

I more than agree. Sprite nude mods nearly always look better to me than 3D models.

I will say, without spoiling chapters 3&4, Deltarune would be an absolutely massive undertaking to nude mod with the drastic increase in content we just got. Starting smaller with just a nude Kris or Ralsei hack would be much more feasible I think. 

Spritesheets are the easiest thing to adjust, you build up from it and mod the game around that nucleus.

The path forward in my eyes is as follows:

 

• Nudify the sprites
• Turn their base designs into something more R rated, maybe give Kris and Ralsei a more femboy edge, add cleavage and chest to the female characters while readjusting their clothes to be sexier.
• Change the story to have more innuendo or even just flat out explicit sex related topics.
• Sex animations come last when you've finally shaped the mod to its fullest.

[losstie27]

47 minutes ago, Buddussy said:

Spritesheets are the easiest thing to adjust, you build up from it and mod the game around that nucleus.

The path forward in my eyes is as follows:

 

• Nudify the sprites
• Turn their base designs into something more R rated, maybe give Kris and Ralsei a more femboy edge, add cleavage and chest to the female characters while readjusting their clothes to be sexier.
• Change the story to have more innuendo or even just flat out explicit sex related topics.
• Sex animations come last when you've finally shaped the mod to its fullest.

 

I don't think any of the characters designs should be outright changed. Not only would that be more to edit, but I think the appeal comes from them being as close to canon as possible.

In terms of story, I was imaging maybe they stay clothed in the light world and lose their clothes when landing in the dark world because it's a nudist world or something. That, again, would cut down on sprites, as well as sort of fit with the themes of the game and dark worlds being a fantasy.

[Buddussy]

4 minutes ago, losstie27 said:

 

I don't think any of the characters designs should be outright changed. Not only would that be more to edit, but I think the appeal comes from them being as close to canon as possible.

In terms of story, I was imaging maybe they stay clothed in the light world and lose their clothes when landing in the dark world because it's a nudist world or something. That, again, would cut down on sprites, as well as sort of fit with the themes of the game and dark worlds being a fantasy.

Sorry, I didn't mean a drastic outfit change ala some sex mods, I meant like the same design, but sexier (tighter clothes, more skin like a midriff window for Noelle or a very low neckline on Toriel to show her cleavage, etc), but if you really want to keep their designs wholly the same, I think the bare minimum would be to give the female characters visible chests on their sprites.

 

An example I'll give is this resprite of Buddy Armstrong from Lisa the Joyful that a friend of mine made.

Edited June 5, 2025 by Buddussy

[Catnatic]

Worked on a little something:

[Buddussy]

5 minutes ago, Catnatic said:

Worked on a little something:

HE'S PULLING HIS COCK OUT

[losstie27]

3 hours ago, Catnatic said:

Worked on a little something:

Awesome!! Is this just something for fun or do you plan on doing more?

[Catnatic]

7 hours ago, losstie27 said:

Awesome!! Is this just something for fun or do you plan on doing more?

Done for fun but I could potentially do the rest of the sprites. Same goes for Undertale.

These sprites are all ripped from the game so it should be pretty easy to reimport these nude edits to the game once they're all finished.

 

On 4/22/2025 at 8:28 PM, losstie27 said:

I feel like the game lends itself fairly well to a nude mod too, with how text-heavy it is. Something similar to your nudity reactions mods for the Pokemon games could work perfectly here I think. The story scenarios there could be really fun to mess around with I think.

Sounds fun but looking into how the game handles dialogue, that's going to be a bit tricky than other games I've edited dialogue in.

Especially if you knew how unorganised Undertale's code is, as every reference to text strings is in one huge script file.

 

If I want to have a character say more things than they originally did, I would have to edit the game's code to call a new custom string of text that I have to manually add to the game's data structure for English text. I also need to learn how the game formats the text as well. I assume "&" is used as a newline but what is the "^2" for?

 

SCR_TEXT:

textdata_en:

Edited June 6, 2025 by Catnatic

[losstie27]

14 hours ago, Catnatic said:

Done for fun but I could potentially do the rest of the sprites. Same goes for Undertale.

These sprites are all ripped from the game so it should be pretty easy to reimport these nude edits to the game once they're all finished.

 

Sounds fun but looking into how the game handles dialogue, that's going to be a bit tricky than other games I've edited dialogue in.

Especially if you knew how unorganised Undertale's code is, as every reference to text strings is in one huge script file.

 

If I want to have a character say more things than they originally did, I would have to edit the game's code to call a new custom string of text that I have to manually add to the game's data structure for English text. I also need to learn how the game formats the text as well. I assume "&" is used as a newline but what is the "^2" for?

 

SCR_TEXT:

textdata_en:

I see! I should've realized Toby's messy code would be a problem there. From a quick google search, I think the SCR_TEXT file is just an internal thing and not actually displayed?? I think the code reads that file to compare it to a different text string that it reads. At least, that's what some guy on reddit said. I also think Undertalemodtool might have a built in string editor but I'm not sure.

If Undertale is a possibility in the future, I'd love to contribute to all of the random NPCs/other one off sprites.

[Buddussy]

47 minutes ago, losstie27 said:

I see! I should've realized Toby's messy code would be a problem there. From a quick google search, I think the SCR_TEXT file is just an internal thing and not actually displayed?? I think the code reads that file to compare it to a different text string that it reads. At least, that's what some guy on reddit said. I also think Undertalemodtool might have a built in string editor but I'm not sure.

If Undertale is a possibility in the future, I'd love to contribute to all of the random NPCs/other one off sprites.

For the sake of anyone who wants to get into it, here's a tutorial for UMMT, with a modded/more featurefull version in the uploader's discord

 

Edit: Looking at the tutorial, I still can get over the chaos of UT and DR's sprite sheets, I dabble in RPGMaker and the sheets those use were never so overstuffed

Edited June 6, 2025 by Buddussy

[losstie27]

6 hours ago, Buddussy said:

For the sake of anyone who wants to get into it, here's a tutorial for UMMT, with a modded/more featurefull version in the uploader's discord

 

Edit: Looking at the tutorial, I still can get over the chaos of UT and DR's sprite sheets, I dabble in RPGMaker and the sheets those use were never so overstuffed

I decided to take a quick look at this tutorial and threw some rudimentary Frisk sprites in game (I don't think I ever realized how much they're shaped like a raw chicken). The tool is actually super easy to use. I can't promise an actual full mod, but something like this would be WAY more attainable than someone like Kris due to how significantly more complicated Deltarune's animations are. As a sidebar, there is a full, working walk animation here, I just obviously can't show it because Loverslab doesn't support gifs.