Deltarune Chapter 3 secret boss guide
Unlike other chapters, the Deltarune Chapter 3 secret boss is hiding in plain sight in Toby Fox’s incredible Undertale sequel, but that doesn’t mean that they’re easy to defeat. We’ve done some digging and uncovered all the tools you need to claim this secret boss’ rewards.
If you need a quick refresher before diving into Deltarune Chapter 3, make sure you take a look at our Deltarune characters guide. Plus, as this game is out on the Nintendo Switch 2, you can get up to speed on the new console with our Nintendo Switch 2 Pro Controller review, Nintendo Switch 2 camera review, and Mario Kart World review.
Here’s everything in our Deltarune Chapter 3 secret boss guide:
Who is the Deltarune Chapter 3 secret boss?
Deltarune Chapter 3’s secret boss is the Roaring Knight. Yes, that’s right – the scripted boss fight after you beat Tenna. While the scripted loss to the Roaring Knight is the standard ending for Chapter 3, there is a way to go back and ‘defeat’ them to earn rewards.
What rewards does the Deltarune Chapter 3 secret boss drop?
The Roaring Knight drops a Shadow Crystal and a Black Shard. The Shadow Crystal is a key item, similar to the other crystals found when you defeat prior chapters’ secret bosses, and the Black Shard is a chip from the Knight’s sword. Kris can equip the Black Shard as a weapon, and it deals massive damage against Dark-type enemies.
How do I beat the Deltarune Chapter 3 secret boss?
To beat the Deltarune Chapter 3 secret boss, you need a special item called the Shadow Mantle. This is the only way to stop the Roaring Knight from one-shotting your characters. Seam mentioned back in Chapter 2 that you would need this item to defeat a seemingly unbeatable foe, but they couldn’t find it to give to you.
It’s also important to note that, even if you’re playing a pacifist route, you have to hit the Roaring Knight to defeat it. The win condition for this fight isn’t killing them, but simply chipping their sword, so it technically doesn’t count as breaking pacifism.
How do I find the Deltarune Chapter 3 Shadow Mantle?
Finding Deltarune’s Shadow Mantle item takes a lot of work and backtracking, but it’s worth it to defeat the Roaring Knight. Make sure to save directly after defeating Tenna but before fighting the Knight so that you can reload at this point later on.
Get S-rank on the first board
First, you need to achieve an S-rank on the first board. This will let you access the S-rank room in the Green Room. Once you’re in there, speak to the NPC to get access to the backstage area and play the minigame on the console.
Level up your sword in the game until you can cut down cacti and trees. Backtrack to the cacti area and break the trees until you go out of bounds. From here, you can find the Ice Key.
Get S-rank on the second board
With the Ice Key in hand, repeat the process, but for the second board this time. Once you’ve achieved an S-rank, head backstage and boot up the minigame again. Level up by defeating lots of enemies, and once you find the raft, use it to sail upwards to a piece of white land.
Here, you’ll find a door with the Delta Rune symbol on it. Enter the temple and you’ll get the White Cloak, which turns your attacks into fireballs. Continue onwards until you reach a locked door. Use the Ice Key to enter the room, and you’ll find the Shelter Key inside.
Go to the shelter
Leave the minigame and head back to the Green Room to trigger the third stage. Play the minigame alongside Susie and Ralsei, leaving the city and going down a manhole to find Undertale’s Toriel. She’ll lead you to the shelter, which you can unlock with your key.
Before fighting the final boss, make sure that you have armor space in your inventory, otherwise, you won’t be able to claim the Shadow Mantle, and you’ll fail the quest. Fight the Shadow Mantle boss, focusing on dodging its attacks until you’re in a good position to attack. Once you defeat the boss, equip the Shadow Mantle as armor for Susie.
The last step is to reload your game just after defeating Tenna, and you should enter the Roaring Knight secret boss fight. You need to deal 25% of its max HP as damage to win and claim the rewards.
That’s everything you need to know to find and defeat the Deltarune Chapter 3 secret boss. For more retro RPGs, check out our list of games like Undertale next, or, if you’re ready to progress, check out our guide to the Deltarune Chapter 4 secret boss.
