If you play Fisch and love late-game content, you’ve probably heard people talking about the Ruinous Oath rod by now. It’s the shiny new toy from the 1.50 “Luminescent Caverns” update (September 20, 2025), and honestly, it’s a monster. We’re talking 95% lure speed, 500% luck, and no weight limit. Yes, you can haul in absolutely anything without worrying about max KG.
Here’s how you can grab the Ruinous Oath rod in Fisch.
Fisch Ruinous Oath Rod Unlock Guide
Step 1: Getting Into the Luminescent Cavern
First, you need access to the new area. If you’re still early in the game, sorry, you’re not getting in. You need to be at least Stage 7+ in Desolate Deep. Otherwise, you’ll just get obliterated.
Once you’re ready, head to Desolate Deep and look for glowing crystals. That’s your hint. The entrance is hidden behind a light puzzle. If you walk in without a lantern or light-based mutation, you’re going to stare at a dark wall and wonder why nothing’s happening. Bring light.
Then comes the Keystone hunt. You need seven of these things:
- Moosewood: under the merchant’s hut bridge.
- Roslit Bay: deep in the coral cave, you gotta swim for it.
- Miners’ Miracle: sitting right on a mine cart track.
- Farmlands: buried near the windmill.
- Stormy Seas: on top of a shipwreck mast. This one made me rage because I fell off like three times.
- Desolate Deep: guarded by a rare anglerfish spawn. Pray for good RNG.
- Lushgrove: top of the parkour vines. Yes, you have to do the parkour.
Take all seven back to the glowing pedestal and boom, you get permanent access. The cavern itself is gorgeous, by the way, but very easy to get lost in. Keep your lantern on unless you like wandering in circles.
Step 2: Unlocking the Crimson Cavern
Inside Luminescent Cavern, just follow the main path until you run into a big locked gate. This is where things get spicy.
You have to solve a crystal puzzle to summon the Crimson Guardian fish. It’s a shiny variant and not too hard to catch if your setup is good, but I had to line up the crystals a couple times before it worked. When you catch it, the gate opens and you get access to Crimson Cavern.
Crimson Cavern is where the game really expects you to know what you’re doing. Fish here hit like trucks and have spawn rates that make you question your life choices. Bring a rod with high luck or resilience. If you have the enchanted Cerulean Fang, this is its moment to shine. If you don’t, bring friends. Grinding this solo is doable but you’ll be here forever.
Step 3: The Shiny Bestiary Grind
This is the part where most players either buckle down or burn out. Talk to the crystal lore-keeper NPC and they’ll tell you to complete the Shiny Bestiary. Which means you now have to catch every shiny variant of the 15 cavern-exclusive fish.
And yeah, the spawn rates are bad. Like 1 to 5 percent bad. You’re looking at hundreds of casts per fish unless you get lucky.
Here’s what helped me keep my sanity:
- Use glowing worms or crystal shards for bait. Yes, they’re expensive, but they save time.
- Equip shiny-boosting mutations. Shiny Magnet and Luck Surge are practically required here.
- Track your progress constantly. If you think something’s bugged, reset spawns by interacting with the Keystone pedestals.
- Collect crystal shards when you see them. They trigger bonus spawns and make things a little less painful.
If you’re going in solo, expect ten to twenty hours of fishing. I did it mostly solo and I was losing my mind by the last three fish. Definitely more fun if you bring a couple friends and complain together on voice chat.
Step 4: Buying the Ruinous Oath
When you finally finish the Shiny Bestiary, go back to the lore-keeper. The rod is yours for 30,000,000 C$.
Yes, 30 million. If you don’t already have that saved up, go farm Abyss Leviathans in Desolate Deep. They’re worth a fortune and will get you to 30M faster than anything else.