Deltarune Chapter 4 Guide - How I Beat the Secret Boss – Hammer of Justice
After finishing Chapter 4 of Deltarune, I stumbled upon one of the coolest hidden challenges in the game: the Hammer of Justice secret boss. It took a bit of digging and some serious climbing, but once you know what to do, unlocking this fight becomes a lot easier.
Let me walk you through how I did it and give you some tips to survive the battle with Susie solo.
🗝️ How to Unlock the Secret Boss
To find this hidden boss, you'll need to collect three music pieces and play them on a golden piano in the Study area (the central room in the Dark Sanctuary). Here’s what I had to do:
Step-by-Step:
- Beat Jackenstein in the Dark Sanctuary. Once you defeat him, you’ll get climbing gear.
- Use the gear to access three hidden climbing areas around the Dark Sanctuary. Each one gives you a piece of a music sheet.
- After collecting all three, return to the golden piano (go through the upper Study door and climb the books by the save point).
- Play the notes that appear — no need to memorize anything! This will open a secret door behind the fireplace.
- Try to grab the Justice Axe inside… and the boss fight begins!
🎼 Where to Find the Three Music Pieces
1. First Piece
From the Study, head left, then follow the path down and left. You’ll dodge magic projectiles until you see a climbable wall. At the top, there's a mini-boss. Beat it to get the first music piece.
2. Second Piece
Backtrack to the magic projectile hallway and go right this time. Go through a long stained-glass hallway until you reach another wall to climb. At the top is a dark statue room — listen for sound cues and flip the light switch to reveal the second piece.
3. Third Piece
Return to the piano area. In the book hallway, there’s a door on the left that leads to a fountain room. Go behind the fountain and climb a wall of bells. At the top, find a second dark passage with the final music piece.
⚔️ How to Beat the Hammer of Justice (Old Man)
This is a Susie-only fight, and it’s not about dealing damage — it’s about surviving and impressing the boss.
Important Tips:
- You can’t hurt him. Every attack will miss.
- Don’t waste turns attacking — use Defend to build up TP, then use OkHeal to keep Susie alive.
- OkHeal is key. Even though healing is weakened in this fight, healing actually moves the fight forward faster than attacking or using Rude Buster.
- Think of the battle like a test — the more you act, especially healing, the faster it ends.
What Worked for Me:
- I equipped Susie with gear that boosted magic and defense. The Absorb Axe really helped.
- I used Defend constantly, only using OkHeal when I had enough TP.
- Don’t panic! The boss patterns seem brutal at first, but once you learn them, you’ll dodge most hits.
- The trick is to stay alive long enough while showing that you’re “worthy” — healing, not hitting, is your best move here.
🏆 Rewards
When I finally made it through, I got:
- 🛡️ The Justice Axe — Susie’s strongest weapon.
- 💎 One Shadow Crystal to add to my collection.
Totally worth the effort.
If you're going for 100% or just love uncovering secrets, this boss is a must-fight. It’s one of the most unique battles in Deltarune Chapter 4, and trust me — surviving it feels awesome.
Good luck!