All Secret Bosses in Deltarune

Deltarune hides one major secret boss in every chapter, giving completionists and battle enthusiasts an extra challenge beyond the main story. As the name suggests, these encounters aren’t easy to find, with each one requiring you to complete specific hidden objectives, solve puzzles, or revisit earlier locations before you can fight them.

While none of these bosses are mandatory, defeating them rewards you with powerful equipment, Shadow Crystals, and some of the game’s most memorable battles. Here’s how to unlock every secret boss in Deltarune Chapters 1 through 5.

Deltarune Chapter 1 Secret Boss: Jevil

Credits: tobyfox

Credits: tobyfox

Credits: tobyfox

Credits: tobyfox

Jevil is the very first secret boss in Deltarune and can be found locked inside a prison deep within Card Castle. Reaching him is simple, but freeing him takes a bit of exploration across the Dark World.

To begin, head to Card Castle and use the south-eastern elevator to travel to the mysterious “??????” floor. Walk downstairs and speak with Jevil in his cell. He’ll tell you that you’ll need the Prison Key to open his door.

The Prison Key is split into three separate pieces. First, visit Seam in the Field and ask about the strange prisoner. Next, travel to the Forest area with the Paper Dancers and take the hidden path leading southwest to find the second piece inside a chest after defeating the Rabbicks. Finally, head north from the Field to the suit-symbol puzzle and enter the correct sequence: Diamond, Heart, Club, Spade.

Once you have all three pieces, take them to Smith Malius at the Bake Sale, who will forge them into the completed Prison Key. Return to Jevil’s cell, unlock the door, and prepare for one of the toughest fights in Chapter 1.

Your reward depends on how you defeat Jevil. Winning through Mercy grants the Jevilstail armor, while defeating him violently rewards the Devilsknife weapon. Both outcomes also grant a Shadow Crystal.

Chapter 2 Secret Boss: Spamton NEO

One step away from becoming a big shot or crashing spectacularly. | Credits: tobyfox

Chapter 2’s hidden boss is Spamton NEO, the bizarre salesman obsessed with becoming a “BIG SHOT.” Unlocking this battle requires following his unusual side quest before reaching the chapter’s finale. When you first encounter Spamton in the alley, avoid defeating him normally. Instead, accept his final deal. Afterwards, visit his shop in the Trash Zone and wait until the price of the KeyGen drops below 100 Kromer before purchasing it.

Continue to Queen’s Mansion and locate the hidden basement by activating the concealed switch behind the potted plant on the first floor. Inside the basement, collect the EmptyDisk from the abandoned robot and bring it back to Spamton. He’ll replace it with a LoadedDisk.

Return to the same machine in the basement and insert the LoadedDisk. As you attempt to leave, Spamton NEO will appear and challenge you. Defeating Spamton NEO rewards either the Dealmaker or the Puppet Scarf, depending on your route, along with another Shadow Crystal.

Chapter 3 Secret Boss: The Roaring Knight

Shows up late, hits hard, refuses to elaborate. | Credits: tobyfox

Unlike the previous chapters, Chapter 3 doesn’t hide its secret boss behind an obscure location. Instead, the real challenge lies in obtaining the equipment needed to survive the battle. The Roaring Knight appears near the end of the chapter after defeating the main boss. Before reaching this point, you’ll want to obtain the Shadow Mantle, which dramatically reduces the difficulty of the encounter.

To unlock the Shadow Mantle, earn S Rank on both TV Time boards. This opens access to the S Rank changing room, where an NPC in the upper-left corner invites you to experience a hidden game. Visit this room three separate times and complete the sequence. During the third visit, you’ll face the Shadow Mantle Holder. Defeat this hidden mini-boss to claim the Shadow Mantle.

Although it’s technically possible to defeat the Roaring Knight without it, doing so is significantly more difficult. Defeating the Roaring Knight awards the chapter’s Shadow Crystal, bringing your collection one step closer to completion.

Chapter 4 Secret Boss: Hammer of Justice

Never argue with a giant hammer. Especially this one. | Credits: tobyfox

Chapter 4’s primary secret boss is the Hammer of Justice, the Darkner form of Gerson Boom. Unlocking this encounter requires finding several hidden collectibles before accessing a secret passage. Early in the chapter, defeat the Jackenstein mini-boss to obtain the ClaimbClaws, which allow you to climb the Sanctuary’s book ladders. You’ll then need to locate three hidden music pieces scattered throughout earlier areas.

One lies west of the room with the patrolling puffballs behind a watery mini-boss. Another can be found east through the stained-glass hallway and the pitch-black room. The final piece is hidden beyond the waterfall inside a bell maze. Once you’ve collected all three, head to the golden piano above the Study and play the completed melody. If you already know the sequence, enter:

Up, Centre, Up, Left, Down, Centre, Right, Centre, Right, Down, Left, Centre.

Doing so opens a hidden passage behind the Study fireplace. Be sure to save before entering, as you won’t be able to use items during the upcoming boss fight. Defeating the Hammer of Justice rewards one of Susie’s strongest pieces of equipment in Chapter 4, along with another Shadow Crystal.

Chapter 5 Secret Boss: Mad Mew Mew

Cute? Maybe. Easy? Absolutely not. | Credits: tobyfox

The final secret boss currently available is Mad Mew Mew, whose battle revolves around collecting a special hidden currency throughout Chapter 5. As you explore the chapter, search every area for 10 Pink Coins. After collecting them all, visit the shop on the cliffside and exchange them for the Mystery Key.

Continue progressing until you reach the final climb toward Flower Castle. Before entering the castle, search the upper area for a locked pink door. Use the Mystery Key to unlock it, revealing the hidden arena where Mad Mew Mew awaits. This fight is one of the chapter’s toughest optional challenges and serves as the final secret boss currently available in Deltarune.

Unlike previous chapters, Mad Mew Mew doesn’t reward a unique weapon or armor piece. Instead, defeating her grants the fifth Shadow Crystal, completing the current collection through Chapter 5. All of these hidden bosses and the general narrative make the game a must-play right now.

Which secret boss gave you the hardest time, and which one is your favorite? Let us know in the comments below!

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