First off, I drew a basic level layout on graph paper. Since I’m going for more of a sidescroller perspective, I showed the map from the side, rather than from the top.

Pretty sure that a real toilet pipe wouldn’t go straight down into an empty room like that, but hey, it’s a game. After the initial layout was done, I put in some basic coloring.

Though this initial coloring isn’t all that bad, I feel it was a touch unfocused, with spots of color thrown in a little too haphazardly. I wanted to differentiate the rooms by color but got a little too extreme with the variation. As such, I’ve revised something a bit more conservative. I break down the new color palette in the image below.

Here’s a collage of reference images I collected. There’s a few pieces of generic sewer art, some from video game levels (Ratchet & Clank, Crash Bandicoot), and some more specific details, such as pipes, steel plating, and grates.

Next up are a few concept sketches for some of the modular elements, as well as the boss object.

I started with a simple large sewer pipe wall that would act as a basic building block for the level. Ill-aligned plate metal covers the curved part, while the flat floor will probably be some kind of concrete. I’ve also considered having pipes lining the walls as a way to break up the monotony.

Next is a smaller tunnel section which acts as a clear break between different rooms. It’s a much smaller and shorter pipe that will probably have a darker coloring. I also include a grate wall surrounded by stonework, to act as boundary the player cannot cross.

Lastly, I threw in a catwalk for good measure, as there’ll be a couple of them to bridge gaps.

At this stage, I’m still hesitant to commit to a direction for the boss object. I considered having him just as a standalone mutated fish, without any metal housing or weapons. If I take this path, I’d have to decide whether he’s just a 2D sprite or a fully fleshed 3D model.

(By the way, I’m going for a Paper Mario-esque style, meaning most characters are 2D sprites. Sometimes the convention is broken for boss characters, who may appear as 3D models for dramatic effect.)

If given a metal housing, it’d definitely be more optimal to model it in 3D. I want to make a quirky, scrapped-together hunk of machinery, with pipes, pistons, and weaponry flailing off it in random directions. A tank in the center would show the shriveled up fish, kept alive only by the ridiculous contraption built around him.

After sketching a concept for a laser, it’s shape accidentally reminded me of a hairdryer. This brought up the idea of designing his weapons as if they were scrapped together from bathroom accessories that somehow made their way down the drain.

In this case, the machine gun is admittedly a bit overkill, but in a universe where toilet drains are direct vertical pipes into a dead-end room, and goldfish can manage to survive in such an environment and foster that much hate and revenge, I don’t think it’d be too out of whack for military-grade weaponry to end up in the sewer somehow.