If you’ve spent any time in the Deltarune community since June 2025, you know the vibes have been chaotic. We finally got the double-drop of Chapters 3 and 4, and honestly, it changed everything we thought we knew about Toby Fox’s formula. While everyone was busy memeing about Mike or Tenna, Chapter 4 snuck in and delivered a final encounter that felt less like a video game fight and more like a fever dream about mortality and legacy.
It's weird.
People are still arguing about the "true" identity of the Deltarune Chapter 4 boss, but the game is pretty literal about it if you’re paying attention. We aren't fighting a TV or a radio this time. We’re fighting the weight of history in the form of Gerson Boom. Or, well, the Dark World’s twisted, towering memory of him.
The Hammer of Justice Explained (Simply)
So, let's look at the facts. The main boss of Chapter 4—the one that actually blocks your path to the Fountain—is technically the "Titan Spawn," but the narrative heart of the chapter belongs to the encounter with Gerson. To be clear, we’re talking about the "Hammer of Justice" battle. This isn't just another wacky Darkner. Gerson was the legendary hero from Undertale, the shopkeeper who knew too much. In Deltarune, he’s been dead for years, buried in the cemetery near Noelle's house.
But the Dark World doesn't care about being dead.
When the fountain opened in the church/graveyard area, it pulled from the "remains" of the greatest smith who ever lived. What we got was a spirit version of Gerson, a massive tortoise warrior who uses "Justice" as a literal weapon. It’s a complete 180 from the goofy Queen or the tragic Spamton.
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The fight is actually mechanical hell. You've got Susie's axe being the primary defense mechanism because Gerson’s attacks aren't just things you dodge. You have to block. It’s a green-soul mechanic, but Susie is the one leading the charge. If you mess up the timing, your axe literally shatters, and you're left scrambling to survive until it "re-forges."
Why this fight is actually terrifying
Most bosses in this game want something from you. They want your SOUL, or they want you to be their gamer-subordinate. Gerson? He just wants to see if you're worthy of the "Prophecy." He treats the battle like a lesson.
The most annoying part? The "Hammer Rain" attack.
Basically, Gerson tilts the entire battle arena 45 degrees. You’re sliding toward the edge while massive hammers fall from the sky. It’s fast. Like, "I need to go to the Dojo and practice for three hours" fast. If you're playing on the Nintendo Switch 2 (where the game launched as a flagship title), the haptic feedback on the controllers actually tells you which side the hammer is coming from. It’s a neat trick, but it doesn't make the pattern any easier to read.
The Secret Boss: Dealing with Mike
You can't talk about Chapter 4 without mentioning the elephant—or rather, the microphone—in the room. While Gerson is the story boss, Mike is the hidden "Bonus Boss." If you thought Jevil was a headache and Spamton NEO was a tragedy, Mike is... something else.
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Finding him involves the "Golden Piano" puzzle in the Study. You have to find three hidden music sheets. Honestly, most of us just looked up the solution on Reddit, but if you do it legit, it takes forever. Once you unlock the fireplace, you find him.
Mike isn't a hero. He’s a "washed-up entertainer" whose attacks are based on sound waves and "cancelled" ratings.
- Static Noise: Fills the screen with gray pellets that move randomly.
- The Mic Drop: A literal giant microphone falls and creates a shockwave you have to jump over.
- Rating Sink: Your TP constantly drains unless you "ACT" to keep the audience's attention.
The interesting thing is how Mike talks about Tenna. He hates him. He calls him a "flat-faced liar." It confirms a lot of the theories we had back in 2021 about the TV world, but it also subverts them. Mike isn't the big bad. He’s just another guy who got discarded when the world moved on to "High Definition."
What Most People Get Wrong
There’s a huge misconception that you need the Shadow Mantle from Seam to survive the Chapter 4 boss. You don't. While the Shadow Mantle helps with the "darkness" debuff in the secret fight, the Gerson fight is purely about rhythm and blocking.
Another weird rumor: that Noelle can "Snowgrave" Gerson.
You can't.
The game won't let you.
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Toby Fox is very specific about the "Weird Route" in Chapter 4. If you try to force a lethal move on Gerson, the game basically tells you that "the hero's spirit cannot be frozen." It’s a meta-commentary on Gerson’s role in Undertale. He was the one guy who knew you couldn't just fight him in the shop. He carries that "invincible" energy into the Dark World.
Tips for Beating Gerson
If you're stuck, quit trying to be aggressive. This isn't a "hit it 'til it dies" fight.
- Focus on Susie: She is your shield. Keep her HP topped off because if she goes down, your ability to block Gerson's arrows disappears.
- The Rico-shell: When he throws the turtle shell, don't just dodge the initial hit. It bounces. It's going to come back from the ceiling. Always look for the star projectiles it leaves behind.
- Don't Stockpile: Gerson has a mechanic where he "confiscates" your items mid-fight. You can only use what you have in the first three turns. Use your best healing items early.
Where do we go from here?
With Chapters 1 through 4 now out and the paid version available for $24.99, the focus is shifting to Chapter 5. Toby’s recent newsletter confirmed that Chapter 5 is targeting a late 2026 release. It's supposedly set in the "Field of Pink and Gold," and it’s going to deal with the fallout of what we learned in the Church.
If you've beaten Chapter 4, your next step is to head back to Castle Town and check the "Special Room." Depending on whether you spared Gerson or "defeated" him, the NPC dialogue changes significantly. Also, make sure you've talked to Sans. He’s got some... choice words about the "old man" returning.
Go back and find the Shadow Mantle if you haven't yet. You're going to need it for whatever is coming in the next update.