In the retro RPG adventure, Deltarune, you take on the role of Kris. Alongside Ralsei and Susie, your mission is to reach the Dark Fountain and seal it. Throughout your adventure, you’ll encounter various characters, confront enemies, and face numerous challenges.
Similar to previous chapters of Deltarune, there are hidden secrets waiting to be discovered by completing certain challenges. While these secrets are typically optional, they often grant you powerful rewards. One such secret in Chapter Four involves an optional boss battle that lets you earn a special weapon for Susie. To find this boss, you’ll begin with a golden piano puzzle.
How to Find the First Part of the Golden Piano Piece
To tackle this puzzle, you first need to obtain a tool that allows you to climb specific walls in the area. Start your search in the room located northeast of Old Man Gerson’s study. After you acquire the tool, return to the initial room and climb the wall to the very top. At the peak, you’ll spot a golden piano waiting for you. You’ll need to come back here after collecting three pieces of a component.
To the left of the piano, there’s a note containing clues about the locations of each part.
For the first piece, make your way to the room with the fountain where you can make a donation. When you donate, the fountain will part for a moment, revealing a hidden door behind it. Enter this door to find yourself in a dimly lit room. Navigate through it and seek out a yellow ripple. Approach it, and you’ll learn it’s a wall made of bells.
Climb up the wall and proceed along the path. You’ll see yellow buttons on the ground; stepping on them will light your way with a yellow ripple. Use these buttons to chart the course ahead until you encounter a blue button. Pressing this button will unveil one portion of the piece.
An enemy that emits a red ripple will then appear and start pursuing you. Quickly retrace your steps along the same path you came from.
How to Find the Second Part of the Golden Piano Piece
To locate the second piece, go back to the door next to the bookcases and the stool where you previously helped Old Man Gerson grab a green book. Head west into the shadowy area filled with moving shadow monsters and blue buttons. In the northwest corner, there’s a wall that you can climb. Ascend to reach the next area.
In this new area, you’ll encounter a climbable wall with water cascading from certain spots. Navigate to the top while avoiding the falling water. At the summit, you’ll find a water-filled container. Interact with it, and when you turn to leave, prepare for a confrontation with a water cooler. Defeat it, and you’ll receive another piece of the component.
How to Find the Third Part of the Golden Piano Piece
For the final piece, return to the door with the bookshelves and stool. This time, head east. Just past the dark hallway with tall windows, you’ll come to another area with a climbable wall. Scale this wall to reach a platform that has a door.
Beyond this door lies another dark area similar to the one behind the fountain. Carefully navigate the obstacles toward a figure on the eastern side emitting a white ripple. It will instruct you to move north to find a short hallway. At the end of this hallway, you’ll discover a yellow button that, when stepped on, reveals the last piece.
Once you have all the pieces, return to the golden piano. When you play it, you’ll uncover a room behind the fireplace in Old Man Gerson’s study. Go back there to find a special item and confront a secret boss.
How to Beat the Secret Boss
Upon entering the room behind the fireplace, you’ll find a powerful axe resting on a stone surface. This is the Justice Axe, which grants Susie an additional 12 attack points. To claim it, you must defeat the secret boss, who turns out to be Old Man Gerson himself.
This fight is tough because Susie will take him on alone, and items cannot be used. You’ll need to rely on your dodging and blocking skills against his various attacks. During the battle, your soul will switch between green and red. When it’s green, you won’t be able to move and will have to block incoming attacks with your axe.
Green Soul Attacks
While your soul is green, you can only move your axe to block incoming attacks from multiple directions. Initially, your soul will be trapped in a box, requiring you to block attacks from the top, bottom, and sides. As the fight progresses, the box will transform into a hexagon, demanding blocks from six directions.
Watch carefully when he fires arrows at you, as their speed varies. Some will approach you more slowly than others, so focus on blocking the faster arrows first.
Another one of his moves involves throwing turtle shells. Pay attention to their colors; the color indicates how many more hits it will take to destroy them. Only when they turn yellow will they require just one more block.
Red Soul Attacks
When your soul turns red, you can move around freely. You can use this opportunity to gain TP by dodging Old Man Gerson’s attacks closely, but be cautious—too much damage isn’t worth it.
One of his attacks has him swing a large green shell at you, causing it to bounce in various directions. You’ll have to dodge both the shell and the star trail it leaves behind. At the end of this attack, he’ll hit the shell from above, showering you with a confetti of small stars that you must avoid.
Another attack will have him hurl dozens of small axes at you for a brief moment before escalating to larger axes, concluding with a single giant axe strike.
His last attack is a swing with his Hammer of Justice. You’ll see the attack zones shine white beforehand, giving you a chance to escape safely.
Susie’s Actions
During the battle, Susie’s attacks may miss but can generate more TP than simply defending. You’ll need this TP because her two actions are crucial for your survival. The only way to heal is through Susie’s Ok Heal, costing 83 TP. Using Rude Buster requires 50 TP, but it can help you end the fight quicker.
When you use Rude Buster, Old Man Gerson will deflect it and send it back your way. You’ll need to hit it back toward him; each time you use this attack, he will deflect it an additional time.
If you manage to win the battle, you’ll be rewarded with the Justice Axe and a Shadow Crystal.