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Version: 30.03

The Underworld
by SkyCorp

The Underworld is a text based forced transformation game for mature audiences including erotic content such as: furry, monstergirl, male to female (MtF) transformation, oviposition, lactation, and more. Along the way, you’ll meet a wide cast of characters across the three factions that each have their own ideology about how to deal with people different from themselves. Your actions will determine which faction achieves victory, and by extension, the fate of humans and hybrids alike.




Just Released: r40 - Succubunny Part II (Private Build)

Explore your new life as Valery's Fuckpet.  In this post-TF content expansion, work to please your new owner as you give into your role as the shortstack's horny female succubunny pet.

This update adds over 10k new words of post-TF Valery & Succubunny content, bringing Succubunny to ~19k words total.  Includes five new saucy scenes -- try to find each one!  You'll need to solve a couple light puzzles to experience them all.  

Also includes a new Sell System -- produce milk and/or eggs and sell them.  Rounding out the update is a number of bugfixes along with a new character backstory for Elijah, the shopkeeper at the Trading Outpost.

See full update notes on the research blog post.


Recently Released: r39 - Shortstack Succubunny TF/TG (Private Build)

Valery, a lowly shortstack drakeling, is determined to make you into her anthro bunny fuckpet.  Not content to merely make you even more of a shortstack than she is, Valery further degrades you into becoming a succubunny (a sexual creature which can only consume cum as food).

This update for active backers includes 9k words of Valery content, plus standalone items for Bunny TF, Succubus mode, and numerous new cursed transformative items.

See full update notes on the research blog post.


Previously Released: r38 - The Whoredra (Private Build)

You had seen the town whore around Haven plenty of times.  A two-headed pink-scaled hydra, she had been affectionately named The Whoredra by Haven's populace.  When you decide to give her a go, you get more than you bargained for when her pimp, Anica, offers a free fuck in exchange for working off the debt.  Anica merges you into the Whoredra's body, making you into the third head of her whore.  You're trapped in the body of a huge-titted, fat-assed draconic prostitute, and you have to share it with two other horny heads!  

Manage the lusty desires of your fellow heads, or they'll wrest control from you and slut around town as they please.  26k+ new words of content.
Full post here.

Fan Art Corner

Dragon Queen (ch3) fan art by Ghostbun

Dinoian (ch6) fan art by HAPPYFACES



r37 - Chapter 7: Aquatic Aquarium Released (Private Build)

Infiltrate the Mulberry Aquarium and become one of the anthro/monstergirl exhibits!  Transform into a horny mermaid, a fat whale, and a powerful shark.  All the while the other creatures in the aquarium seduce you in front of a rapt audience of tourists and visitors.  Will you accomplish your mission and escape the aquarium... or just become one of the lusty wildlife?
The largest chapter update ever in Underworld history!  Full post here.

r36 - Mermaid TF & Water (Private Build)

Become a lusty, buxom mermaid in r36!  That heavy mermaid tail will keep you stuck in the water, and being a horny merslut, lust attacks will hit you for double damage.  But unlike humans, you can breathe underwater.  Currently, you'll be stuck in a test pool with the octomaid, but she knows just how to keep you company with those tentacles ;)

Full post here.

r35 - Wyvern Male & LUA Powered Monsters (Private Build)

Encounter the Wyvern Male, a monster who is eager to turn you into his breeding mate.  He'll take good care of you, ensuring you're knocked up with eggs and milking your four large tits when they grow too heavy.  The wyvern is quite a dominant partner, and will remind you of your place... and thanks to your new breeder instincts, you'll find yourself becoming quite submissive to him and his dual cocks.  He has about 7k words of content (roughly the entire length of Chapter 2!) for a fun variety of scenes.

Modders also gain a range of new tools, including the ability to create LUA powered monsters and entity-to-entity communication.

Full post here.

 r34 - In-Game Mod Browser / Mod Portal (Private Build)

You can now easily browse and install mods -- all from right from inside the game!  Full post here.

Browse interface:

Details interface:

 r33 - Female Breeding Wyvern TF (Private Build)

Become a female breeding wyvern in the newly released r33 build!  Fight against (or give into :3) your new mating instincts as you become a horny quadruped with a huge, egg-filled belly.

Full release notes here.

 r32 - Chapter 7 Intro (Private Build)

You finally make contact with the shadowy Baosheng Group and discover Krista is becoming a cowgirl.  Will you return her to human, send her to the farm, or keep her for yourself?  These three different endings will greatly affect the future of VCiV.

Also includes proper tracking, display, and save/load for the Faction Point system.

Full release announcement here.

 r31 - Teasing Tentacles (Private Build)

  • Shark TF - Become a powerful anthro shark!
  • Tease system allows NPCs to tease you based on your new body.
  • Octomaid, a half-octopus sea monster who knows just where to put those tentacles of hers...

Full blog post here, including some more details on the tease system.

r30.03 - New public demo build

A new public demo build is now available!  Since the last demo build, this includes:

  • Tattoos & Piercings system - Get one to force yourself to always be lusty, or prevent your breasts from ever decreasing in size.  You could even get one to get rid of those pesky attack options so you have to always submit to your opponents...
  • Choose initial acceptance level - There are now three options during character creation to decide your initial acceptance rate and how you treat others. Each option has its own little intro story to go with it, along with an explanation of the acceptance system.
  • Better organization of inventory UI.
  • More reliable keyboard shortcuts.
  • Numerous other small improvements and fixes.

r30.01 - More Modding Support / Wolf TF (Private Build)

r30 is released, including new transformation features for modders. A Wolf TF sample mod is available to demo the new quadrupedal/paw support for modded transformations. Also, don't forget to check out the Dragon Queen enemy mods by Saint!

r29 - Permanent Tattoos (Private Build)

r29 adds support for Permanent Tattoos that make you more obedient, lusty, or cause other effects.

r28 - Piercings (Private Build)

This update features a piercings system for wearable piercings that cause various effects to your character.  

Want to force yourself to always be lusty, or prevent your breasts from ever decreasing in size?  Or wear one to get rid of those pesky attack options so you have to submit to your opponents...

r27 - Choose Initial Reaction (Private Build)

There are now three options during character creation to decide your initial acceptance rate.  Each option has its own story to go with it, along with an explanation of the acceptance system.  One of the options even lets you TF Becky some more ;)

r26 - Map Mods / Spider Dungeon (Private Build)

Can you steal the treasure from the spider nest and escape? Or will the spiders get the best of you and transform you into their mate, forever filling you with brood after brood of spider eggs...

The new Spider Dungeon map demonstrates the new support for Map Mods, allowing you to create your own maps to explore in the game.

r25.01 Dinoian Fixes (Private Build)

The Underworld r25.01 is now released - I accidentally broke the Dinoian chapter in the previous release, so if you had trouble with that, please grab the new build.  Also includes some other misc dinoian chapter text fixes & save fixes

r25 Modding Requests (Private Build)

r25 adds a number of features requested by modders.  You can also check out our first user-created transformation (Pig TF by Luxious) if you like weight gain stuff, including both a Pig King enemy to fight and a cursed transformation pendant.

r24 Transformation Mods (Private Build)

You can now mod your own transformations into the game, including the first transformation mod: Anthro Giraffe TF.  The r24 build also includes a new auto-login system which will be especially useful for Android players, along with an update to the game's business model.  Additional details on the blog.

r23 Mod Support for Items + Clothes (Private Build)

r23 is now released to all private backers and includes the ability to mod in your own items and clothes into the game!  These can be simple text-only mods, or can be driven through LUA code.  There’s a number of new sample mods available, including the cursed weight gain pendant which will cause you to gain weight continuously.

r22 (Public + Private Builds)

The main new content for public build players in r22 is Frog TF:

Now the frogs in the swamp chapter can now transform you into one, too.

4000+ words of chapter 2 content including different scenes when the Naga Queen defeats you based on what form you’re in. The minions are a bit smarter too, and won’t try to transform you if you’re already a frog or slug (unless you’re not 100% in that form, in which case they’ll try to re-transform you if you’re of the matching species). Frogs and slugs also now leave a slime trail wherever they go, which can re-transform you if you use it (it’ll eventually evaporate). If you track slime into Nixie’s shack during the swamp quest, she’ll comment on you making a mess of her place.

Frog form is another in the all-fours category, since frogs can’t stand upright. As frogs naturally gain weight over time to get that nice frog belly, that can eventually cause their movement to be difficult. At larger belly (and optionally breast) sizes, it will drag on the ground beneath them and sometimes get stuck in the slime as they travel. If you go farther and intentionally max out belly/breast sizes... good luck moving at all.

Additional New/Updated Functionality:

  • UI Updates / DPI-aware layout
  • Wait Button
  • Entity Selector
  • Retuned Dragon Queen oviposition rules
  • Added reduce cream to hospital shop, and as an item occasionally dropped by foxgirls.
  • Misc text fixes

r21 (Private Build)

Chapter six: "Dinoian Desert" is finally complete and ready to play!  r21 is available for download for all full game / private build backers at the researcher intranet in both SWF (PC) and APK (Android) flavors.

This build includes the release of the Dino Chapter.

At the conclusion of chapter five, you incapacitated Thornton by transforming him into a catgirl, leaving him trapped to work in Mulberry's strip club while you steal his identity.  You're now able to sneak into his convoy, which will allow you to cross the vast underground desert to scout out SkyCorp's research laboratories for the rival faction, VCiV.

What should have been an easy ride across the desert turns out to be much more than you bargained for.  The convoy rides on specialized creatures that are genetically engineered to withstand the tough conditions of the desert.  These dinoians could best be described as a distant anthropomorphic cousin of a velociraptor, or perhaps some sort of wingless riding dragon.  One of them, Hanako, is planning her prison break, and you haplessly stumble into her plans.

Soon she's stealing your identity.  She forces you to wear her old leather bindings, transforming you into a dinoian that looks just like she used to.  She had unintentionally acquired the reputation of convoy slut, and now that you have her identity, she intends to make sure you live up to her old behaviors so as to not be suspicious.  Every time you disobey her, she increases the size of your cleavage, making you hornier as you're forced to expose your nearly-naked body to the world as she rides you.  To make matters worse, thanks to your monstrously large dinoian vagina, you won't derive any joy from copulating with humans -- so your body will work against you to force yourself to mate with your fellow beasts.  But they're in a similar predicament, former humans trapped in lusty bodies that have no choice but to serve their riders and their base desires.

Try as you might, dinoians are forbidden from speaking thanks to their vocal cords which can only make animalistic noises.  Though you desperately want to explain your situation, no one can understand you.  Even removing the bindings themselves is impossible as they self-replicate to ensure you can never be freed.  Stick around long enough, you'll start to enjoy serving your rider.  You may even begin to enjoy being tied up with your wrists bound, further restricting your opportunities for escaping this life.

Will you succumb to your dinoian need to be filled up and lay clutch after clutch of eggs?  Or will you find a way to escape your fate and complete the mission?

Backstory is revealed about the history of The Underworld, along with the factions that vie for power inside it.  Three endings, one for each faction, are available -- each with their own puzzles to complete.  Can you find all three?

Clocking in at a massive 30,000 words, this chapter is nearly three times as long any that has come before!

Finally, I'd like to say thank you for everyone's kind words and encouragement during this massive chapter's development, whether that be in blog comments, discord, or wherever.  I've never tried writing anything this huge before, and I couldn't have pulled it off without you cheering me on.  So thank you, and I hope this chapter brings you much enjoyment.

Past update summary

  • r5 [public] - UI improvements, including the popularly requested customizable font size [details]
  • r6 [private] - Weight TF system - Eat food to replenish HP, but if you over-eat you will gain weight which will make your belly difficult to conceal [details]
  • r7 [private] - Panda TFs - Transform into a panda [details]
  • r8 [private] - Cowgirl TF - Transform into a cowgirl, lactate, at high levels grow an udder [details]
  • r9 [private] - Chapter 4: Cowgirl Farm - The next story chapter, which includes forced TF into cowgirl [details]
  • r10 [private] - Shop system [details]
  • r11 [public] - Bug fix & public build [details]
  • r12 [private] - Added Elephant TF, Cat TF, and multi-breast TF (five new transformation items total). [details]
  • r13 [private] - Chapter 5: The Pound (Catgirl Stripclub TF) [details]
  • r14 [private] - Horse TF (horsedick / autofellatio), Tiger TF (multibreast), Turkey TF (inflation) [details]
  • r15 [public] - Public release of: Horse TF, Tiger TF, Turkey TF, multibreast items.  Also adds portable milker.  [details]
  • r16 [private] - Mobile / Touch support & APK build [details]
  • r17 [private] - Female Spider TF (egg laying) [details]
  • r18 [private] - Monster Mods, Male Spider, Custom Name Entry [details]
  • r19 [private] - Save support [details]
  • r20 [public] - Public release of: Cloud Save/Load, Custom Name Entry, Mobile/APK Support [details]
  • r21 [private] - Chapter 6: Dinoian Desert, Frog TF, UI Updates, Wait Button [details]
  • r22 [public] - Public release of Frog TF
Login: nixie
Password: *****

.// Welcome to SkyCorp Employee Mainframe //--
MOTD has been updated by root in the past seven days

> motd

Attention! All SkyCorp employees are to be alerted of outbreak of VIR-819 in Mulberry and surrounding areas. Original infection of virus into human populace traced to -REDACTED-.

Progressive exposure of the virus causes mutagenic effects in human subjects. Infected are highly contagious, causing additional mutagentic effects on humans they contact. So far, documented mutagenic effects have included: hybrid fox transformation, hybrid dragon transformation, increased libido, gender changes, and oviposition. Due to the chaotic nature of VIR-819 and the denizens of the Underworld, the infected are likely to encounter all prior mutagenic effects listed. Additional mutagenic effects are expected as the virus evolves.

SkyCorp has lobbied and received regional government funding to build the Underworld, an underground complex where infected creatures are mandatorily required to relocate to upon discovery. Investigative journalists have indicated this network contains at least one shantytown, a sewer dungeon, some sort of mysterious temple, and various connecting passageways. However, SkyCorp personnel must strictly occupy only the town of Mulberry and other overworld areas for their own safety, unless they have received designated security training. Additional areas are expected to be found as exploration of the network continues in future.

Employees should encourage Mulberry citizens to be ever vigilant of signs of infection. Infected creatures have been known to mask their mutations with clothing and feign humanity -- but these creatures are dangerous and must not be allowed to run free due to their changed nature. SkyCorp has identified at least one suspected sympathizer in town who has been providing aid.

Employees interested in researching The Underworld/VIR-819 are requested to download the training materials.

A recent copy of Adobe Flash will be required (Flash 11+), and employees are requested to file a summary report on their experience in Mulberry and surrounding areas. Prospective trainees are advised as to the early and experimental nature of this program.

> logout

Latest Reviews - View All Reviews

Review by Shaing

Version reviewed: 40 on 04/07/2021

First of all, if you read this:

Do NOT "buy" this game or support this developer.

That being said, what is "The underworld"?

Its a furry MTF sandboxy fetish game that, credit where credit is due, is being build from the ground up. The focus of the game is of chapters with a differnt TF each time with "puzzles" to escape and progress the story.

What is "The underworld" aswell?

Its a cash grab. Worse then candy crush, raid shadow legends and EA. Basicly like many others that wrote reviews here thus far, i bought this game years ago when there were only 2-3 chapters with the idea that as time passed more content was released and the game would be refined. Let me make myself clear. What i paid for, was a COMPLETED GAME. At first, progress even looked fine, even if slow. But that changed soon as the first few new implementations were made. By this point this "Project", I wont even call it a game anymore, combines the worst parts of gaming that popped up everywhere recently. A single player game with always online requirement, access to mods behind a paywall and the modders dont even get a cut (which is particular scummy), Day -1 DLC (again, the game is far from finished but there are still 2 "DLC" updates that only are there to get you to spend more money) and a freaking subscriptions basis so if you want to support the dev and get a nice game in return, too bad, you only get to keep it a month. 

Just how money hungry the dev really is becomes clear when the last story update was over 2 years ago and there is not even a mention of any work being done or even begun in that direction so by this point, there really only is a need to check in every year or so to be dissapointed again.

Never the less, the worst part of this experience truely is the fanbase this person build around themselves. Their community is just plain toxic, worse then even CS:GO or LoL and you truely dont want to be a part of that.

So PLEASE stay clear of this dumpsterfire and support better games and better devs on this site that actually deserve your time and money or even artist that do all sorts of kinky stuff but here it would only be wasted and even worse yet, encourage this bad behaviour.

Review by Leymoon

Version reviewed: 38 on 09/08/2019

While this was an exceptional game, with surprisingly good content and detailed transformations, even playable game overs, I would really just two or three versions ago(~v36) wholeheartedly approve of this game. In the past I would have said "the demo should at least be tried by everyone" as well - now it's best to avoid due to temptations and disappointment.

Personally I really liked the Dragon Queen and Dinoian chapters a lot, with the oviposition involved, while the cow chapter was to me the least interesting... and I would have jumped right on to the Whoredra dlc if it had not been a permanent 'requires subscription' thing... such a shame it's come to this.

...then it became obvious that the dev seems to have something against people who don't or can't pay constant subscrition. At first, backers got most content. Then you could pay once to get access to the 'dlc' content. Now you need an active subscription to access dlc content. I'm willing to pay when I can, when I can at least keep what I paid for. To me the ideal monetization would be much like so many others do nowadays, as in a "pay-per-update"-ish way, keeping the version available at the time subscribed, but needing to resubscribe when a new update arrives. Demo being public, and main game/dlc could still be a pateron thing, hell non-story content could even be a higher tier for all that matters... that would be so much better. And less pushing away to potential one time backers. however, unfortunate as it is, it seems like such a compromise or alternative isn't even something they'll ever accept even considering.

Considering that backing for this game has (apparently) been slowy dwindling over the last half year, I can only HOPE the dev actually understand that their agression has gone too far, before it's too late... just please, SkyCorp, if you read this, learn to understand that being too narrowminded and stubborn isn't going to help.


Bottom line and fair warning: If you try this and like it, it is pretty much the only one single player game out there that will require constant subscription every time you desire to play it.

Review by foxdsx

Version reviewed: 37 on 07/10/2019

i did try this game a few years back and actualy forgot it by the next day.

paying for this trash is foolish


Review by meem

Version reviewed: 37 on 07/09/2019

not recommended till it drops the price. i probably wouldn't shell out that much for this unless it was highly praised, let alone having to pay that much per month. public/free version has far less content than the private branch and hasn't been updated recently.

Review by grimtriad

Version reviewed: 37 on 04/13/2019


Please don't play this game, don't support this developer, and don't encourage this kind of abusive behavior towards our community.


I had paid for this game years ago when it was still relatively new giving the author the benefit of the doubt.  It was expensive based on the state but also had some hard to find content that I really enjoy (forced non-human TF).

The agreement with that purchase was that I would recieve future content for free as I supported the game.  Patreon came out about a year later and things started to change.  The first change was to create what is effectively DLC, so that the developer could start charging for content other people created.  As if this wasn't irritating enough, most of the content was advertised on TFGS as new content, and not as DLC that required a subscription to get.

So I eventually caved, picked up a subscription as one piece of content was really appealing only to learn the dev has multiple levels of BS.  Instead of just having Patreon charge me up front and adding me automatically, a script has to run, and will only run near the begining of the month after I pay.  So even if you want to play the DLC content, you have to wait until the dev gets around to letting you...  So, after realizing I would have to wait a month (as this dev consistently puts out updates shortly after the month starts) I backed out of the pledge as I already didn't like that I was paying a second time for something that felt should be provided with the core game (if the dev wrote it) or for free.  This is literally the same way the players feel when day 0 DLC hits or when devs start charging for for player created mods, except, the game isn't out yet and yet it already has DLC...

As if this wasn't enough abuse to people that have already shown their support, I'm now locked behind a time gate for new content as I'm a legacy user...  Instead of showing respect for the people that were willing to overlook the obvious flaws, I feel like I'm getting spit on instead. 


This dev is a real piece of work.  Please do not support them.

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Total Reviews: 16,782
Total Engines: 33
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