Rain World audio design stories: Part 3 - More slugcats

Rain World

The story of the Rain World modding community continues, developing into an official partnership with Akupara Games on the Downpour DLC.

Be sure to check out Part 1 and Part 2 of this deep dive.

By Jerry Jeriaska (The Ongaku) and Eric Bratcher.

Rain World's modding scene took off shortly after the launch of the base game, leading to the establishment of a user-generated content hub dubbed 'RainDB'.

One ambitious, unauthorized add-on was Side House, a mod undertaken by programmer AndrewFM and sound designer Connor Skidmore. Gathering up unused maps located in the Steam deliverables and integrating custom threat music, the demo served as a proof of concept for building out the in-game environment.

Designer Joar Jakobsson and music composer James Primate at Videocult gave a boost to the RainDB community by bundling an official map editor with the 1.5 update. However, behind the scenes, the intellectual property was entangled in legal red tape, tying the hands of the game studio and jeopardising prospects for further development.

As weeks of innovating on Rain World mods stretched into years of commitment, AndrewFM came to wonder if the collaborative journey of the More Slugcats mod was predestined to end in disappointment. Here, we are afforded a glimpse into the challenges entailed in this off-the-beaten-path endeavor.

More Slugcats depicted by James B Barrow.

Touch Fuzzy, Get Dizzy

On the heels of Connor's involvement in the Side House project, additional audio designers began volunteering to contribute background music to the More Slugcats expansion

Composer Andy Robison, known on RainDB as Progfox, recalls: "[AndrewFM] already had this huge, elaborate plan for expanding on the earlier modding project that he made into this full-blown fan-made campaign. At the time, I was so enamored by the game that I wanted to be involved in any way possible."

AndrewFM began by sharing a Google doc, detailing the plans for each of the custom regions planned for the expansion. "We also created a mood board," he relates, "where we grabbed a bunch of reference images with what we wanted to do and the aesthetics of these regions. A lot of the music tracks were produced based on these mood boards and written descriptions."

To satiate the appetite of the playtesters, Progfox uploaded a preliminary track titled "Bloom" to SoundCloud. "Every now and then we would drop little things to show that something's happening," he says, "because in these kinds of projects things get picked up and dropped all the time."

Progfox · Bloom - Rain World 'More Slugcats' Downpour Expansion OST

Progfox observed of the base game's score by James and Lydia of the band Bright Primate: "There are so many times where you enter a new area and there's a part of the soundtrack that was created to represent what's going on, to help push you forward a little, or give some color to the scene going on. I think that Rain World isn't afraid to use silence. It pushes these big, emphatic moments when they really matter. It was cool to be able to create something that acts as a moment, and not necessarily an ongoing vibe."

Meanwhile, AndrewFM and Connor began experimenting with modifying threat music when the player slugcat eats a mushroom. These consumable items introduced to the game by Joar induce subtle psychoactive effects that temporarily increase the slugcat's run speed and jump height. Most noticeably, the visuals undulate hypnotically. AndrewFM relates, "We wanted the threat music to change slightly or use different tracks when you are under the influence of the mushrooms."

Ultimately the developers dropped the mechanic because it would have required creating extra threat layers for every region of the game. As with the unused regions recycled in Side House, this was a thread the More Slugcats team left dangling.

"That implementation is programmed into the game," AndrewFM notes. "Modders, if they wanted to, could make use of that."

Rain World
Gourmand character portrait by AnnoyingFlower.

Rarefaction Cell

As time passes in Rain World there is an overarching theme of survival strategies evolving from offensive to defensive. The slugcat breed known as Rivulet reflects this progression by exhibiting increased maneuverability. The amphibious critter demonstrates the agility of a coiled spring on land and can hold its breath for long durations while plunging underwater. To complement the aquatic theme of the campaign, the devs went back over familiar maps, introducing drizzling rain and overcast skies.

This damp era of Rain World's history adds a speedrunning element to the mix, as the cycles between game-ending torrential downpours are considerably shorter. Rivulet hibernates sooner due to these shorter cycles, and also occasionally wakes up early. These "pre-cyle" showers offer the player a glimpse of the environment before the rain has fully let up. Walls of water cascade, blurring the scenery and obscuring drenched predators, before intermittently subsiding.

Rivulet's campaign was the inspiration for the goal of creating one new region for each of the playable slugcats. The submerged iterator superstructure was the first custom region designed from scratch, making unique use of Rivulet's ability to remain underwater.

Upon reaching the decaying iterator complex, the aquatic slugcat gains access to a rarefaction cell capable of producing a spherical low-gravity field. This glowing orb's visual effects were contributed by co-composer Ongomato.

"He was very multi-faceted," AndrewFM relates. "He did music, but that was not the thing we brought him on for. He was primarily a technical artist. He created shaders and 3D models: all the cool, fancy effects that you find in the expansion, like the snow and the blizzards."

Several music tracks, such as "Daze" and the "Outer Expanse" threat music, involved collaboration between the composers. "I think that between the three of us, we all sort of filled gaps in each other's skill sets," observes Progfox. Ongomato went as far as to construct a rendering pipeline that allowed the developers to take 3D models and convert them into 2D, embedding them in the scene.

"He made detailed 3D models and then injected that into the 2D scene," says AndrewFM. "He did a lot of cool stuff for the expansion."

Grapple Worm

Rain World The Saint
The Saint by AnnoyingFlower and region art illustrator Tom "Norgad" Starbuck.

The Saint's campaign brings certain elements of the story full circle, such as expanding upon the Void Sea location first introduced at the end of Survivor's campaign. "There's this giant ocean of corrosive liquid that exists deep down below the earth," AndrewFM explains. "Saint takes place so far in the future that much of the structure has dissolved away from the Void Sea. That opens up a new area that the other slugcats don't have access to."

Saint is frail and relies on a long tongue to latch on to platforms and flee from predators. To implement this gameplay feature, the developers reverse engineered the grapple worm mechanic. In place of having to seek out and hijack this seldom encountered creature, this slugcat breed has evolved to integrate tongue-slinging into its own anatomy.

While the Saint can maneuver vertically by latching onto ledges and whip across chasms, this campaign features dual hazards of running out of food and falling victim to the harsh environment. A cruel winter has beset the land, requiring the slugcat to seek out lanterns and steam vents to restore body heat. The Saint's head-up display adds a hypothermia bar that will signal the onset of frostbite.

The iterator superstructures' copious heat energy vents are collapsed during the Saint's epilogue, taking place long after the others. Navigating this Ice Age, the player encounters a terrestrial environment that has returned to its desolate appearance predating the terraforming efforts of the Ancients.

Progfox · Daze - Rain World: Downpour OST ft. Connor "12LBS" Skidmore


In February of 2021, AndrewFM received an email from Akupara Games. "What they had noticed was despite Rain World going this really long length of time without receiving any updates, the community was still more active than it had ever been," he recalls. "It still was escalating in popularity, despite the game not receiving any updates. They immediately saw that as something they wanted to continue fostering."

Videocult had finally regained access to the IP from the former owners. Akupara Games' CEO David Logan had spearheaded an official partnership in an effort to greenlight new content for Rain World. AndrewFM wound up submitting a synopsis video, clocking in at just under three hours in duration, introducing More Slugcats' new regions, spanning a thousand new maps. The video also outlined the Challenge and Safari modes, building upon the Arena contents.

Based on this synopsis, it was decided that the More Slugcats expansion would be included in an official downloadable contents release, dubbed Downpour.

Rain World Downpour

Downpour soundtrack cover art by character portrait illustrator AnnoyingFlower.

Outer Expanse

While reviewing previously designed maps and remixing them with weather elements like rainfall and snowstorms, the team decided to build out the Chimney Canopy region. This smallest self-contained area in the game contains a partially flooded subregion called The Gutter, which was expanded upon and treated to its own alternate audio layers for threat music.

Artificer and Gourmand were the last slugcat campaigns to wrap up development. Taking place shortly after Spearmaster's timeline, the Artificer is capable of fashioning explosives from rocks and spears at the cost of food. The slugcat can even propel himself forward using a detonation as a makeshift double-jump, gaining access to out-of-the-way ledges.

A bitter feud between this particular slugcat and the tribes of scavengers makes the character's pyrotechnical acumen crucial for survival. As with other campaigns, the backstory behind this chapter's drama slowly unfolds as the player progresses. Uniquely, this story is elucidated over the course of several playable dream sequences.

"Gourmand's campaign is essentially a scavenger hunt for food," AndrewFM explains. The hefty slugcat can weaponize his girth by dropping on predators from above to incapacitate them. While running, Gourmand is winded easily and is required to take a breather to recover full speed.

After visiting Looks to the Moon's crumbling superstructure, Gourmand is allowed to explore the surrounding Outer Expanse region, now reclaimed by nature. "Our idea with the Outer Expanse is that the Ancients built these rail systems and didn't care about the abandoned ruins from past civilizations," says AndrewFM. "You have these train tracks that demolish or plow their way through these old ruins. There's an amalgamation of past civilizations in these barren outskirts."

The developers identified this sanctuary as an appropriate spot to implement a day/night cycle. "The original game does have a very few sections where you are safe from the rain threat, but there are very few," AndrewFM observed. "With the expansion we added more of those types of areas. For those, we wanted to have something special that happens. There is a cycle progression going on, despite the absence of the rain."

For the first time, a character under the player's control can travel back to the location where Survivor's animated intro is situated.

The Artificer character portrait illustration by James B Barrow.

Having leant her voice to the base game, Lydia offered to revise the dialog of Looks to the Moon and other speaking parts. These revisions helped to ensure greater thematic continuity across the old and new campaigns. When it came to the lore, AndrewFM was sensitive to the demands of the fanbase not to stray too far from the premise outlined by Videocult.

"There were a lot of people in the Rain World community who are picky about the lore," he relates. "If you go too wild, there are people who will get upset. Anything we include is stuff that is a very direct extension of what is already there."

In the run-up to the release of "Downpour," RainDB member Intikus stitched together several trailers, writing custom music that appears in the soundtrack album release published through Bandcamp. "There was a lot of polishing going on," AndrewFM recalls of the discovery that "More Slugcats" would soon be a commercial product. "Once we did find that out, we had to go back and be like, "Okay, is there anything here we should polish up or improve?"

Progfox, credited as the lead soundtrack producer for the official expansion, remarks, "Back then, it was a bit of a fanfiction, adding in your custom-colored characters and giving them fun abilities. You would not have imagined that being transformed into something official." Connor adds, "Even back then, I dreamed of it one day being taken on as an official expansion, but I never imagined that it could actually happen."

James Primate is a video game composer – brightprimate.bandcamp.com | Twitter @BRIGHTPRIMATE | Spotify artist page

AndrewFM is a video game developer - ko-fi.com/andrewfm | Twitter @AndrewFM

Connor Skidmore is a video game composer - soundcloud.com/12lbs

Progfox is a video game composer - progfox.io | Twitter @ProgfoxMusic | Spotify artist page