How to defeat Watercooler boss in Deltarune Chapter 3 and 4

The Watercooler boss in Deltarune isn’t exactly a major story boss, but it still stands out thanks to how often it shows up and how strange the whole thing is. It first appears in Chapter 3 and returns in Chapter 4, turning into a running joke — but with actual fights involved. If you're not prepared, you might get caught off guard.

Here's where to find it in both chapters and how to deal with it properly.

Note: The article reflects the writer's view; as a result, slight gameplay variations may occur.

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How to defeat the Watercooler boss in Deltarune Chapter 3 and 4

Gameplay still from Deltarune (Image via Toby Fox)

Chapter 3 location

You’ll first run into the Watercooler boss in Deltarune inside the C-rank room in the Green Room during Chapter 3. This is between the rounds of the weird game show Kris, Susie, and Ralsei are forced into by Mr. Ant Tenna. The encounter seems small at first, but don’t ignore it.

It shows up again later in the same chapter. After beating Shadowguy and the two Pippins, you’ll go through a stealth section with spotlights. Then there’s a garbage-filled room, followed by more spotlights. After that, you’ll reach a door up north. Once you go inside, the Watercooler will be waiting near a chest.

If you try to walk away without fighting, more Watercoolers will spawn each time you re-enter that door. Keep going in and out, and eventually you’ll get cornered into a battle.

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Chapter 4 location

The Watercooler boss in Deltarune returns in Chapter 4, just after you beat Jackenstein. While climbing up a section with water pouring on you, head toward the upper-left corner during the second climb. There’s a large wooden water container here. Interact with it — you’ll get a short bit of dialogue, and the Watercooler jumps out to start the fight.

There’s also a smaller appearance later in Chapter 4. After you reach the big pipe organ, go right, and you’ll spot a bunch of Watercoolers. As you walk past them, Mizzles jump out.

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Battle strategy for Watercooler boss in Deltarune

Duel with the Watercooler boss in Deltarune (Image via Toby Fox)

In the Watercooler battle, you’ll have three ACT options — Flirt, Act Cool, and Beg for Mercy — but only Act Cool actually helps you end the fight. Flirt changes the Watercooler’s colour and adds some humour, but doesn’t increase Mercy, and Beg for Mercy won’t work unless the name is already yellow. Keep choosing Act Cool to steadily raise the Mercy bar; a few more tries should make the name turn yellow so you can spare it.

Its main attack drops raindrops from different angles, which all gather into a large ball of water at the center of the screen. Sometimes the ball stays still, but sometimes it moves left to right. You’ll need to dodge both the drops and the ball itself, but overall, the pattern is simple enough to get used to.

Throughout the fight, Suzie smashes cups while Ralsei keeps things tidy, adding some fun to the encounter. Flirt adds personality, but Act Cool is what gets results.

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That concludes our guide for the Watercooler boss in Deltarune.

Check out: How to defeat Roaring Knight secret boss fight in Deltarune Chapter 3