Honestly, nobody saw the Gerson comeback coming like this. We all knew the old turtle was a legend in Undertale, the shopkeeper who basically laughed in your face because he knew you couldn't touch him in a menu. But in Deltarune Chapter 4, the hammer of justice deltarune lore takes a sharp, emotional turn that completely shifts how we look at Susie’s character arc. It’s not just a boss fight. It’s a passing of the torch.
If you’ve been scouring the Dark Sanctuary looking for that one missing piece of the Golden Piano puzzle, you know the Drill. You find the sheets, you play the tune, and suddenly you’re face-to-face with the spirit of Gerson Boom. But he isn't just "Gerson" anymore. He’s the Hammer of Justice, and he’s about to put Susie through the absolute ringer.
The Secret Boss Everyone Is Stressing Over
The hammer of justice deltarune encounter is easily one of the most mechanically unique fights Toby Fox has ever dropped. Usually, Deltarune is a team effort. You’ve got Kris for acts, Ralsei for heals, and Susie for the muscle. Not here. This is a Susie solo mission.
You find him behind the fireplace door in the Study. Susie, being Susie, tries to just grab the "Justice Axe" off the wall. Typical. Gerson stops her and demands a "haircut" as payment. Since she can't actually cut his hair (because he's a spirit/Darkner hybrid made of memories and old metal), the fight kicks off.
It’s a Green Soul fight. Remember Undyne from Undertale? It’s that, but on steroids.
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Why the Green Soul is Different Now
In the past, you just had four directions to block. Up, down, left, right. Simple. Gerson doesn't play that way. He introduces diagonal blocking. You have to hit two keys at once to tilt Susie’s axe to a 45-degree angle. If you’re playing on a keyboard, your fingers are going to be doing some serious gymnastics.
- The Octagon Shift: Halfway through, the box turns into an octagon. Arrows come from eight different sides.
- The Hammer Break: A massive hammer comes down from the top. If it hits your shield, it literally shatters it, forcing you back into the Red Soul mode to dodge Gerson himself.
- The Star Shell: He launches a "copyright-free" turtle shell that leaves a trail of stars. It’s a mess of projectiles that feels more like a Touhou game than a standard RPG.
What Most People Get Wrong About the Justice Axe
There’s this huge debate on Steam and Reddit about the reward for this fight. When you finally outlast Gerson (you can’t actually kill him, you just have to "impress" him), you get the Justice Axe.
Its stats are wild: +12 Attack. That’s huge for Chapter 4. But then you look at the description and it just says "Ability: ???" and "You obtained this weapon by BECOMING STRONGER."
A lot of players are frustrated because the axe doesn't seem to do anything special in battle. No fire magic, no TP reduction, nothing. But they’re missing the point. The "??? Ability" isn't a weapon perk. It’s a permanent buff to Susie’s base stats. If you pay attention to her "BetterHeal" or "OkHeal" after this fight, the TP cost starts dropping. Gerson isn't just giving her a piece of metal; he’s teaching her how to actually use her magic.
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The real reward is that Susie finally stops trying to be a "brute" and starts becoming a hero.
The Lore Connection: Gerson, Undyne, and the Author
Toby Fox loves his motifs. The song "Hammer of Justice" is packed with references to "Spear of Justice." It makes sense—Gerson was Undyne’s idol and mentor in the other timeline. But in Deltarune, Gerson is dead. He’s a memory.
The dialogue in this fight is some of the heaviest in the game. He talks about his book series, Lord of the Hammer, and how he wrote six chapters but couldn't finish the seventh. He says the story "swallowed the author up." That is 100% a Gaster reference, or at the very least, a meta-commentary on Toby Fox himself.
He asks Susie how she thinks the story should end. Susie, in her typical style, says "Eternity." Gerson laughs and tells her to "write her own ending." This is a massive hint that the "Your choices don't matter" theme is about to get flipped on its head. Susie is the wild card. She’s the one who breaks the rules of the game.
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Surviving the Hammer: Quick Tips for the Struggle
If you’re stuck on the Star Shell phase, you aren't alone. It’s the hardest part of the fight.
- Don't Attack: Seriously. Rude Buster is a waste of TP here. You cannot damage him. Save every bit of TP for "OkHeal."
- Focus the Closest Arrow: In the Green Soul phase, the arrow that is about to hit you first will turn red. Ignore the others. Only look at the red one.
- Perfect Blocks: If you time your block right, you get 1% TP instead of 0.5%. It doesn't sound like much, but in a solo fight where you need to heal constantly, it’s the difference between life and death.
- The Triangle Pattern: During the Rico-shell attack, move Susie’s soul in a rough triangle shape. It helps you stay ahead of the star trail without getting cornered.
The hammer of justice deltarune boss is a test of patience. It’s Gerson teaching Susie that a hero isn't someone who hits the hardest, but someone who stands their ground when everything is falling apart. By the time the screen fades to white and Gerson tells you it’s the most fun he’s had in years, you really feel like you’ve earned that +12 Attack.
Go back to the library after the fight. Talk to Alvin. There’s some new dialogue about his father’s hammer that’ll probably make you misty-eyed if you’re a long-time fan of the series.
To wrap this up, make sure you've equipped the Mystic Band before heading into the fireplace. That extra defense is the only thing that makes the octagon phase survivable for most players. Once you have the Justice Axe, head back to the main path—Susie’s new magic scaling makes the rest of Chapter 4 a lot more manageable.