All Deltarune Secret Bosses and How to Unlock Them (Chapters 1-4)
Exact locations, item requirements, and trigger conditions for every hidden boss across the current chapters.
Exact locations, item requirements, and trigger conditions for every hidden boss across the current chapters.
by Shivam Malani
Every chapter of Deltarune hides at least one optional boss that you will almost never stumble into by accident. These fights are harder than anything in the main story, and most of them reward you with a Shadow Crystal plus unique gear. Several also have a hard cutoff, so if you leave a Dark World without triggering them, they are gone for that save.
Quick answer: Each secret boss requires a short side quest before you can fight it. In order, the bosses are Jevil (Chapter 1), Spamton NEO (Chapter 2), Shadow Mantle and the Roaring Knight (Chapter 3), and Hammer of Justice and Mike (Chapter 4). Trigger each one before leaving its chapter’s Dark World.
Jevil (Chapter 1, Card Castle)
Jevil fight (Image via Toby Fox)
Jevil is locked in a cell beneath Card Castle. To reach him you need to repair a key that has been split into three Broken Key pieces. You can take him on at any point once you reach the Castle, and you do not have to finish the chapter first.
Ride the Card Castle elevator to the first floor, then find the second elevator that leads to a floor marked with question marks. Walk to the cell at the end and talk to the prisoner inside to start the search for the key.
Return to the Field and visit Seam’s shop. Choose the “Strange Prisoner” dialogue option, which is highlighted, to receive the first Broken Key piece and hints toward the other two.
Find the second piece in the Forest. In the area filled with Ballerinas, head southwest into the hidden passage (there are no stars there) and open the chest waiting at the end.
Bring all three pieces to Smith Malius at the Bake Sale, who will combine them into a working door key. Return to the cell gate and use it to start the fight.
Important: defeat Jevil before you beat the Chaos King. Once King falls and the chapter ends, you cannot return to the cell. The reward depends on how you finish the fight.
Reward
How you finish
Effect
Jevilstail
Actions only (pacify)
+2 AT, +2 DF, +2 Magic
Devilsknife
Fighting only
+5 AT, +4 Magic, Buster TP Down
Either route also grants a Shadow Crystal, the rare item that drops only from each chapter’s secret boss. Both equipment rewards carry over into later chapters.
Spamton NEO (Chapter 2, Queen’s Mansion basement)
Spamton NEO fight (Image via Toby Fox)
Spamton NEO waits in the basement under Queen’s Mansion. You must trigger him before you finish the chapter, because the fight becomes unreachable once you leave the Cyber World. The setup runs through Spamton’s secret shop in the Trash Zone, which only opens if you defeated him earlier by acting rather than attacking.
After reaching Queen’s Mansion, use the Warp Door to travel to the Trash Zone. Head left and go north through the hole in the wall to find Spamton’s shop, which only Kris can enter.
Buy the KeyGen from him. Its price constantly changes and can swing wildly, so keep backing out and clicking it until it lands at a price you can afford. Pick up anything else you want now, since the shop closes for good later.
Return to the Mansion and go to the easternmost room of Floor 1F, past the traffic puzzle, which is filled with Queen statues and paintings. Interact with the blue vases (or follow the Hacker if you finished his blue checkmark quest) until a hidden basement passage opens.
Take the left hallway to the last door, which looks empty until a teacup ride appears. Ride down, flip the switch to drop the forcefield, then ride back up.
Head right down the newly opened passage to the room with roller-coaster tracks. In the second room, interact with the decrepit robot to collect the EmptyDisk.
Return to Spamton in the Trash Zone and hand over the disk. He writes over it and gives back a LoadedDisk, warning that the shop now closes permanently.
Go back to the robot, insert the LoadedDisk, and interact with it. When you step into the room with the tracks, Spamton confronts you and the fight begins.
Shadow Mantle (Chapter 3)
Shadow Mantle fight (Image via Toby Fox)
The Shadow Mantle is Chapter 3’s secret boss, and beating it is also the step that lets you defeat the Roaring Knight later. The whole sequence hinges on getting access to the backstage room behind the green room. You can reach it by earning S-ranks, and if you keep missing that, getting the lowest possible score for a Z-rank leads to the same place.
Earn an S-rank in the first round of Tenna to unlock the green room. If you fall short, you can buy a rank from the NPC south of the green room, but only once.
Take the left door at the top of the green room and talk to the NPC at the big door to enter backstage. Move left and complete the minigame to obtain the Ice Key.
Earn an S-rank in the second round, then return backstage. Use the raft to sail upward into the forest area until you reach a temple with a Delta Rune on the door. Enter it and take the White Cloak, then explore further to find a Shelter Key behind a locked door.
Visit the green room a third time and head backstage with Susie and Ralsei. Follow Toriel, then use the Shelter Key to open the Shelter and trigger the Shadow Mantle fight.
Note: This is your last window for the chapter’s hidden content. Once you continue the story past this third backstage visit, the path softlocks. The win condition is a damage threshold, not surviving a set number of turns, and you can only fight here. Defending with Kris and Ralsei to build TP and spending it on Susie’s Rude Buster every turn is the cleanest approach. Bring revive mints, since the fight has a quirk that knocks party members out.
Roaring Knight (Chapter 3)
Roaring Knight fight (Image via Toby Fox)
The Roaring Knight appears automatically during the Chapter 3 story and is brutally hard on a normal run. To actually beat it, you need the Shadow Mantle armor first.
Reload your save from immediately after defeating Tenna, then take on the Roaring Knight with the armor in place.
Hammer of Justice (Chapter 4)
Hammer of Justice fight (Image via Toby Fox)
The Hammer of Justice is Chapter 4’s secret boss, and it turns out to be Old Man Gerson. Reaching him requires solving a piano puzzle using three hidden music sheets, plus the ability to climb walls.
Collect the three music sheets. The first is in the Waterfall Room, the second is in the room where the message about Jockington’s beard appears, and the third is in the Tea Room.
Return to the Study and climb up to the Golden Piano. Play the notes in this exact order: Up, Center, Up, Left, Down, Center, Right, Center, Right, Down, Left, and Center.
When the tune finishes, a hidden door opens by Gerson’s fireplace, leading straight into the boss fight.
Mike (Chapter 4)
Mike fight (Image via Toby Fox)
Mike is the second secret boss in Chapter 4, and the toughest to qualify for. You can only challenge it if you recruited every possible Darkner back in Chapter 3.
Step through the door to start a conversation that leads into the fight against Mike.
The pattern across every chapter is the same. A weird character or out-of-the-way room sends you on a short fetch quest, and the payoff is a Shadow Crystal plus gear you can carry forward. The biggest risk is missing the window, so trigger each boss before you leave its Dark World, and keep a clean save before each fight in case it takes several tries.
