Chapter 1: Jevil
Jevil waits in a cell beneath Card Castle. Collect the three Broken Key pieces across the Field and Forest, have Smith Malius forge them into a key, and unlock the cell — before the Chaos King, or the chapter ends and the fight is lost. Beat Jevil for the Jevilstail (pacifist) or Devilsknife (violent) and a Shadow Crystal.
Chapter 2: Spamton NEO
Spamton’s secret fight is the most famous in the game. Buy the KeyGen from his shop in the Trash Zone (the price fluctuates), force your way into Queen’s Mansion’s basement, swap the EmptyDisk for a LoadedDisk, and step into the roller-coaster room to face Spamton NEO. This one is Kris-only and famously difficult.
Chapters 3 & 4: four more bosses
Chapter 3 hides Shadow Mantle (unlock the backstage Shelter with the Ice Key and Shelter Key, then win a damage-threshold fight — its armour is needed for the next boss) and the Roaring Knight (reload after Tenna with the Shadow Mantle equipped on Susie). Chapter 4 adds Hammer of Justice (find three music sheets and play the Golden Piano sequence) and Mike (recruit every Chapter 3 Darkner, finish the credits, reload, then enter code 6453 on Mike’s Room door).
Chapter 5: Pink
The newest secret boss is Pink, the final Shadow Crystal bonus boss in the Flower Kingdom. Finding her means collecting ten Pink Coins and using the Mystery Key on the hidden door. Guides on the exact coin spots are on IGN and Destructoid. Every secret boss drops a Shadow Crystal, and several drop unique gear — track them down before leaving each chapter’s Dark World.
Player questions
How many secret bosses are in DELTARUNE?
Seven across the five released chapters: Jevil, Spamton NEO, Shadow Mantle, the Roaring Knight, Hammer of Justice, Mike and Pink.
How do you fight Jevil?
Collect three Broken Key pieces in the Card Kingdom, have Smith Malius forge the key, then unlock the cell beneath Card Castle before defeating the Chaos King.
How do you unlock Spamton NEO?
Buy the KeyGen from Spamton's shop in the Trash Zone, use it on the forcefield in Queen's Mansion's basement, complete the EmptyDisk/LoadedDisk sequence, then step into the roller-coaster room.
Who is the secret boss of Chapter 5?
Pink — the final Shadow Crystal bonus boss, hidden in the Flower Kingdom behind the Mystery Key and the ten Pink Coins.