Splatoon 4 Hidden Secrets & Collectibles: Sunken Scrolls, Sardinium & Everything Worth Finding

I'm just going to say it, the Sunken Scrolls are the best lore delivery system in any Nintendo franchise. They're not just collectibles. They're single-page fragments of a post-apocalyptic story told through ancient human artifacts, research notes, and propaganda posters. And half of them are hidden in places you would never find without backtracking through levels you already cleared. That's the whole appeal.

In Splatoon 3's Alterna hub, there were 24 Sunken Scrolls scattered across the overworld and inside specific kettle levels. Each one a piece of a larger puzzle about what happened to humanity, how the mollusk era began, and the true nature of Alterna itself. The one that stuck with me was a diagram of the Alterna rocket, the same rocket where you fight the final boss, drawn in the style of a 1960s aerospace blueprint, annotated in Japanese. That's the level of detail we're dealing with.

Finding them all took me about three weekends of focused hunting. And yes, I used a guide for the last four. No shame.

The other big collectible type is Sardinium, which in Splatoon 3 was the upgrade currency for hero gear. Each piece of Sardinium let you unlock or upgrade one node on the hero weapon's skill tree, things like increased ink capacity, faster charge time, and damage boosts. There were enough Sardinium pieces in the campaign to fully upgrade every hero weapon, but only if you found all of them. Missing even one meant leaving some upgrade incomplete.

Sardinium in Splatoon 3 hid in two places. Some were in the overworld, tucked behind inkable walls, inside snow mounds you had to shoot away, or on ledges you could only reach with specific sub weapons. Others were inside kettles as hidden collectibles, you'd see a fish-shaped icon in the level select that told you a level had Sardinium you hadn't found yet. That icon was the only hint. Some of the kettle placements were genuinely cruel. One piece in a Splatling-focused level required you to shoot a target through a tiny gap while riding a moving platform. If you missed, you had to restart the whole level to get another shot.

There were also the data logs scattered around Alterna. These were different from Sunken Scrolls, they were text logs, research notes from the humans who built Alterna, explaining what they were trying to do and why it failed. They're the closest thing the series has to a traditional audio log collectible, and they're all optional. You could finish the campaign without reading a single one. But if you're like me and actually care about why the Splatoon world exists, they're essential.

Let me talk about lockers too because this is a collectible system most people don't think about as collectibles. In Splatoon 3's multiplayer lobby, you got a personal locker you could decorate with items earned from the catalog, Salmon Run, and the single-player campaign. Stickers from finding all the collectibles in a kettle. Figures of boss Salmonids. Weapons and gear to display. The locker became a trophy room for everything you'd done in the game. Some players turned their lockers into elaborate dioramas. Others, like me, just threw everything in and called it a day.

The Splatoon 4 equivalent will almost certainly evolve this. With the Switch 2's capabilities, maybe more interactive locker items, or the ability to visit friends' lockers more seamlessly. Nintendo loves taking a small feature from one game and making it central in the next. Look at what happened with the photo mode.

Now about the hero weapon replicas. In Splatoon 3, completing every kettle in the campaign unlocked hero replicas of the multiplayer weapons. These were visually distinct, they had the hero skin, all worn and modified-looking, but statistically identical to their multiplayer counterparts. The grind was real but the payoff was mostly cosmetic. If you're a completionist, do it. If you're not, don't stress. The replicas don't give you any competitive advantage.

The secret kettle was always a thing in Splatoon campaigns. After finishing the main story, a hidden kettle would appear, usually the hardest level in the game. In the Octo Expansion it was Inner Agent 3, a boss fight against a superpowered version of the player character from Splatoon 1. In Splatoon 3 it was After Alterna, a gauntlet of brutally difficult platforming sections that ended with a combat arena. These secret levels exist to humble you. I spent four hours on Inner Agent 3 before beating it and my hands were shaking by the end. No joke.

If Splatoon 4 follows the pattern, expect a secret final kettle that makes the rest of the campaign look like a tutorial. These levels are where the devs take off the gloves and design the hardest thing they can justify including. The Octo Expansion's secret boss was so notorious there are still YouTube guides being made for it years later.

For collectible hunters specifically, Splatoon 4's campaign will likely have some new twist on the system. Maybe collectible map fragments that assemble into a larger picture revealing a secret area. Maybe gear ability chunks hidden in the overworld as an alternative to the multiplayer grind. Maybe lore movie reels, Splatoon 3 had memory chips you could view, and upgrading those to actual animated scenes would be a natural Switch 2 evolution.

One thing I always do on my first playthrough of a new Splatoon campaign: don't look anything up. I play through once blind, beat the final boss, then go back with a guide to find everything I missed. The first run is for the story and the experience. The second run is for the completionist itch. Both are valid. Doing it in that order means you get both.

If you're the type who wants 100% on your first try, I respect the hustle but I'd argue against it. Some of the best moments in Splatoon campaigns are stumbling into things you weren't looking for. A Sunken Scroll you found because you shot a random wall out of frustration. A hidden path that opened up because you inked a corner that looked suspicious. Those moments don't happen when you're following a checklist.

Whenever Splatoon 4 gets here, the collectible hunt will almost certainly be deeper than anything the series has done before. It always is.