Deltarune: How to beat Hammer of Justice secret boss in Chapter 4

Deltarune Chapter 4 is packed with new challenges, secrets, and intense battles, and one of the most exciting ones is the Hammer of Justice, a hidden boss fight. Defeating him rewards players with powerful items like the Justice Axe and Shadow Crystal.

This guide will explain how to beat the Hammer of Justice secret boss in Chapter 4 of Deltarune.

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How to unlock the Hammer of Justice boss fight in Deltarune

The Hammer of Justice is one of the most memorable secret bosses in Deltarune (Image via Tobyfox | YouTube/@Hawlo)

To access this secret fight, you must solve the Golden Piano puzzle. But first, you have to unlock the ability to climb.

1) Getting the climbing ability

Play through the main story until you face the Jackenstein boss. Defeating him rewards you with Climb Claws, which let you climb walls. Once you’ve got them, return to the Study Room, the place for solving the piano puzzle.

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2) Solving the Piano Puzzle

You must find all three music sheets to play the full song on the piano:

• Music Sheet 1: Go to the waterfall room with the donation box. The sheet is hidden behind the waterfall. But remember that you’ll need to load an earlier save if you’ve already completed the Sanctuary.
• Music Sheet 2: Head to the dark area where the message “Jockington grows a beard” appears. Climb the wall in the upper-left corner to find the sheet.
• Music Sheet 3: Go near the Tea Room, then walk backward from the Study Room to find a hidden side path. Take it to get the third sheet.

After acquiring all the sheets, return to the Golden Piano and use the three sheets to play the full tune. Once successful, a secret passage opens. Head down and find a door with a hammer symbol. Inside, you’ll see the Magic Axe.

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3) Defeating the Hammer of Justice

Touching the Magic Axe triggers a cutscene: an old man appears and challenges you to a battle. If you accept, he transforms into the Hammer of Justice boss, and you'll have to defeat him.

Face the Hammer of Justice in a duel as Susie, where timing and precision are everything (Image via Tobyfox | YouTube/@Hawlo)

Fighting as Susie, use Rude Buster to trigger a minigame where you must block arrows and falling hammers with your axe. You must time your blocks carefully, as mistakes will cause heavy damage. The boss will parry your attacks, so you must parry to land hits.

As the fight progresses, attacks become faster, so stay focused. Keep the rhythm and parry at the right time to wear him down and defeat him.

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If you win against him, you'll receive the Justice Axe and Shadow Crystal. A short cutscene also plays where the old man shares a story with Susie, comparing her to the Dragon from a legend.