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There’s a second secret boss in Chapter 4 of Deltarune — an optional fight that’s so purely experimental and silly, most of us will never even attempt it. If you’ve been recruiting monsters, you’ll have a chance to fight the unseen Mike mentioned often but never actually shown in Chapter 3, and Mike isn’t just one little guy. There are three Mikes and to beat them, you’ll need to use a very weird gimmick. You’ll need to speak into a microphone and make a whole bunch of noise. Yes, really.
For the more traditional secret boss in Chapter 4, learn how to fight the Hammer of Justice here.
How To Open Mike’s Door

If you recruit Pippins, Shadowguy and Zapper in Chapter 3 (by using MERCY) they’ll appear in a secret room at Castle Town.
- In Castle Town, go to the TV building. Inside, go to the left-most door. It’s locked.
- To open the door, input the code: [6-4-5-3]
After putting in the code, you’ll enter a puzzle room full of cat statues. The goal is to pet all the cat statues in the room — but some can’t be reached.

- Cat Statue Room Solution: Pet the cat statue next to the Maus enemy. This unlocks the ability to use your mouse cursor to reach cat statues and pet them.
Pet all the statues to unlock the door to the Mike Zone. Here, you’ll need to use the Crystal Ball to calibrate your microphone volume — yes, really, this battle requires a microphone. After calibrating, you’ll need to get through a door.
- How To Open The Mike Zone Door: To open the door, you must speak loudly into your microphone. If you speak loudly enough the door will open.
There’s a reason for all of this. The boss inside requires you to use the microphone to win. At least on PC — on Switch / PS5 you’ll use the [ZR / R2] buttons respectively. Interact with the large microphone before the boss to change mic settings — you will be able to set the microphone to a button instead. Technically, that means this boss fight is MUCH EASIER when you don’t have to use your own voice, as you won’t have to make constant noise to properly fight this boss.
How To Beat Mike

To fight Mike, you’ll only need a microphone (or a hot-key) and your mouse.
- You don’t have many choices in this fight. Clicking Mike will progress and take you to the next battle sequence — clicking your characters heals them.
- Making noise will move the heart to help you dodge attacks and survive.
You can’t use items or really make any choices. There are three Mikes and each one has different gimmicks to their battle scene — avoid damage and pet the Mikes when they appear. Keep going until all three Mikes attack at the same time and combine. For their final attack, they’ll try to smash you — keep clicking on them to finally beat Mike.
Defeating the Mikes unlocks three mini-games you can play with your mouse controls and microphone.
This is a ridiculous, gimmicky optional battle that’s sillier than anything else in the main game. And now you know how to try it yourself.