Deltarune Chapter 3 Secret Boss Fight Guide (Roaring Knight)
Written by Aarav Agarwal
You can fight the secret boss in Chapter 3, but you’ll need to take a very specific path through both main rounds first. It’s not technically the weird route, but it definitely feels like it at times.
You’ll know you’re on the right track when things start getting a little too quiet.
How to Start the Path to the Secret Hidden Boss in Chapter 3
Get S Rank on the Cooking Board
To start the route, you need to earn S-Rank on the cooking minigame in Round 1. This unlocks a special door near the upper-left lounge in the S Rank hallway.
Talk to the guard at the door, then head inside. This begins the hidden chain that leads to the Roaring Knight fight.
Clear the Beta Game and Kill Everything
Inside the secret room is a retro-style “Beta” game. Play through it and defeat every enemy you can find. Once they’re all gone, you’ll hear a familiar jingle. This powers up your sword and also unlocks a hidden path.
In Beta 1, chop into the forest to open the path. You’ll find the Ice Key in a hidden chest. If you need help on getting the Ice Key, you can see a video below by Accelerated Ideas on YouTube.
Continue Through Round 2
S-Rank Again
You’ll also need S Rank in Round 2 to keep progressing. Explore every room and collect as many items as you can. If you’re short, some players have reported that enough tokens can be used to buy your way in.
Follow the Cloaked Figure
After clearing Round 2’s Beta game, follow the small cloaked figure. Don’t go off-path or skip ahead. You’ll be guided to another hidden zone, where you’ll unlock another key. Once done, head back to the Green Room.
You’ll now have access to the final hidden Beta level.
The Final Beta Game
Beat the Hardest Beta Level
The third and final Beta game is the toughest. Long attack sequences, tight dodging, and tough enemies. Survive and push through until the end.
At the end of this fight, you’ll receive the Shadow Mantle. Equip it immediately. You need it to unlock what’s next.
How to Fight and Beat the Secret Boss in Chapter 3
The secret boss appears automatically later in the story if you have the Shadow Mantle equipped.
You’ll know you’re in it when everything shifts and you’re locked in with a tall, shadowy knight.
How the Fight Works
You can’t just rush the boss down. This is a hybrid of survival and damage thresholds.
Kris should Act to boost speed early
Susie should wear the Shadow Mantle and tank hits
Ralsei needs to guard or he’ll get one-shot (poor guy)
Use healing items wisely and learn the boss’s patterns. Some attacks can be dodged consistently once you get the rhythm.
When the boss turns into a black silhouette, keep trying to hit them… There’s no obvious feedback, but it’s required to end the fight.
If you survive long enough and do enough damage (felt like ~75% to us, but we’ve seen players say as low as 20% and some say as high as 60%), you’ll reach the ending phase.
Win, and you’ll get a Shadow Crystal and a powerful item tied to the Knight’s blade… the Black Shard.
What is the Black Shard?
The Black Shard is a unique weapon for Kris that gives +16 AT and adds the Slay Dark effect, boosting damage against dark-element enemies. It appears automatically in your inventory and stays equipped in both worlds, though its description changes depending on where you check.
You can’t miss it after the fight, and you definitely won’t forget the fight it took to earn it.
Final Blurb
Chapter 3’s secret boss is less of a side detour and more like a shadow hiding right in the middle of the main path. If you follow the clues and survive the brutal final sequence, you’ll walk away with one of the hardest-earned rewards in the game.
FAQ
Q: How do you unlock the secret boss in Chapter 3?
Get S-Rank in both main rounds, complete the hidden minigames, and equip the Shadow Mantle.
Q: Is this part of the weird route?
No, it's not the weird route. It feels close, but doesn't count as one.
Q: Can you miss the boss if you don’t equip the item?
Yes, you must have the Shadow Mantle equipped to trigger the boss fight.
Q: How hard is the secret boss?
It’s one of the hardest in the series. Long patterns, high damage, and no room for mistakes.
Q: What do you get for beating it?
A Shadow Crystal and a rare, Knight-related item.
Q: Is this fight optional?
Technically yes, but it ties into major story themes, so it feels essential.
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