Deltarune Chapter 4 Walkthrough

Chapter Overview

Deltarune Chapter 4 takes the party to the Dark Sanctuaries, a sacred and solemn Dark World filled with books, bells, stained glass, and prophetic murals. The tritagonist of the chapter is Gerson Boom, a returning character from Undertale who helps the party — and eventually becomes one of the game's toughest secret bosses.

First Sanctuary

The chapter begins in the First Sanctuary. After outrunning the Titan Spawn, the party meets the Old Man (Gerson), who asks for help reaching his study. Susie reluctantly agrees, and the group escorts him through the sanctuary.

Key items and events:

• WaferGuard and ScarfMark: Found in the Old Man's study. The ScarfMark is a useful weapon for Ralsei before the final boss.
• AbsorbAx: In the room north of the bookcase room, solve the green and blue block puzzle to reach a chest containing this vampiric axe for Susie.
• MysticBand: Move the green block to the leftmost part of the same room and climb the ladder to find this magic-boosting accessory.
• Money Pool: Donate Dark Dollars for rewards. Donating 9,999 D$ grants the Gold Widow armor; lower amounts give healing items.

After Susie builds a DIY project (the Couch Cushion for Ralsei's room) and the party defeats the Jackenstein mini-boss, you receive the ClimbClaws, which allow you to scale book-ladders and reach previously inaccessible areas.

Second Sanctuary

The Second Sanctuary introduces moving pianos, sound-based rooms, and new enemies like Winglade and Organikk.

• Use the moving piano to smash through old bookshelves and create new paths.
• Harmonize with the circle of statues to spare Organikk enemies peacefully.
• Climb towers with Susie, using charge jumps and avoiding falling water. Grab her hand for boosts when prompted.

Third Sanctuary

The Third Sanctuary is the final area before the chapter's climax. Before facing the final boss, ring the bell to check whether you have spared everyone you could. If not, backtrack and recruit any missing enemies.

You can also race the Annoying Dog back at the First Sanctuary via a green flame teleport. You cannot win, but you earn a single Dog Dollar for trying.

Final Boss: The Titan

The Chapter 4 final boss is the Titan, a massive creature of prophecy. The battle has multiple phases and requires the party to fight from both outside and inside the Titan.

Key mechanics:

• When the Titan begins healing repeatedly, Gerson appears as the Hammer of Justice and helps Susie use Dual Buster to weaken it.
• Use your strongest attacks and keep the party healed. The fight is long but pattern-based.

Secret Boss: Hammer of Justice

The Chapter 4 secret boss is Gerson Boom as the Hammer of Justice. This is a Susie-only battle and one of the hardest skill checks in the game.

To unlock the fight:

1. Defeat Jackenstein and obtain the ClimbClaws.
2. Collect three music pieces hidden in the chapter:
   • West, past the room of patrolling puffballs, behind a watery mini-boss.
   • East, through the stained-glass hallway and a pitch-black room.
   • Behind a waterfall through a maze of bells.
3. Return to the Old Man's study and climb the bookshelves to reach the golden piano.
4. Play the correct melody: Up, Neutral, Up, Left, Down, Neutral, Right, Neutral, Right, Down, Left, Neutral.
5. A secret path opens behind the Study fireplace. Interact with the Magic Axe.

The fight itself plays like Undyne's battle from Undertale: block Gerson's attacks by moving the soul into the correct directions, then strike when you have an opening. Victory rewards the Justice Axe (+12 Attack) and the Chapter 4 Shadow Crystal.

Optional Items & Secrets

• Princess Ribbon: In the book-attack room, rush to the top-right corner and navigate a hidden jumping puzzle.
• PowerBand: Complete the Cup Challenge climbing room.
• Tension Gem: In the underwater climbing section, let the current carry you down to a hidden path.
• Chapter 4 Egg: Found in a long hallway in the Second Sanctuary.

Chapter 4 Completion Checklist