Undertale Route Guide: Combat, Secrets, Endings

This guide explains the three main routes in Undertale (Pacifist, Neutral, and Genocide), how to handle combat in each, the secrets that unlock the true ending, and how your choices determine which ending you see. You’ll learn the exact actions needed for each route, what to do if you make a mistake, and how to avoid common pitfalls.

Understanding the Three Routes

Undertale’s story branches based on whether you kill monsters, spare them, or flee. The game tracks every encounter, and your overall behavior determines the route:

• Pacifist Route: Spare every monster, never kill anyone, and complete specific friendship events. This leads to the best ending.
• Neutral Route: Kill some monsters, spare others, or flee. This is the default ending, with variations based on who you killed.
• Genocide Route: Kill every monster in every area, including required boss fights. This leads to a dark, meta-ending that permanently alters the game’s files.

Your route is not locked until late in the game, but early choices matter. For example, killing any monster in the Ruins prevents the Pacifist ending on that file.

Combat Basics and the ACT System

Combat in Undertale is turn-based, but you control a small heart (your SOUL) that must dodge attacks. Each turn, you can choose FIGHT, ACT, ITEM, or MERCY. The ACT menu is key to sparing monsters without fighting. Every monster has a specific action (or sequence of actions) that makes their name yellow, allowing you to spare them.

For example, to spare Toriel, you must repeatedly use the “Spare” option until she stops attacking. For Papyrus, you can use “Flirt” or “Joke” to lower his HP, then spare him. For Undyne, you need to flee from her chase sequence and then use “Cool” or “Heat” in the final battle. Always try new ACT options; the game rewards experimentation.

Pacifist Route: Step-by-Step

To achieve the true Pacifist ending, you must do the following:

1. Never kill any monster, including bosses. Always spare or flee.
2. In the Ruins, spare Toriel by choosing “Spare” repeatedly (even when she tells you to go).
3. In Snowdin, befriend Papyrus by visiting his house after the date/hangout.
4. In Waterfall, after defeating Undyne, go back to her house and give her water (use the glass of water in the room).
5. In Hotland, hang out with Alphys at the lab (after the Mettaton EX fight).
6. After the final boss of the Neutral route (Photoshop Flowey), reload your save and go to the lab’s true lab to complete the story.

If you accidentally kill a monster, you can reset the game (from the menu) to start over. However, a true reset is needed to clear the game’s memory of that kill.

Genocide Route: What It Takes

The Genocide route requires you to systematically kill every monster in each area until the game tells you “But nobody came.” This means you must grind in each area until the random encounters stop. Key points:

• In the Ruins, kill all monsters (including Toriel) before moving on.
• In Snowdin, kill all monsters (including Papyrus).
• In Waterfall, kill all monsters (including Undyne, who transforms into Undyne the Undying).
• In Hotland and the Core, kill all monsters (including Mettaton NEO).
• The final boss is Sans, who is extremely difficult.

This route is intentionally brutal and changes the game’s ending and post-credit scenes. It also permanently alters the game’s files (a “soulless” mark) that affects the Pacifist ending if you reset afterward.

Neutral Route and Its Variations

Any playthrough that doesn’t meet the strict criteria for Pacifist or Genocide is Neutral. This includes killing some monsters, sparing others, or fleeing. There are many variations based on which bosses you kill. For example, if you kill Papyrus but spare everyone else, you get a different ending phone call than if you kill Undyne. The game encourages you to explore these variations, but the Pacifist ending is considered the “true” ending.

Secrets and Hidden Content

Undertale is famous for its secrets. Some notable ones:

• The True Lab: After a Neutral ending, you can access the True Lab by going back to Alphys’s lab. It contains lore about the Amalgamates and the game’s backstory.
• Gaster: A mysterious character (W.D. Gaster) who appears in hidden rooms (e.g., the door in Snowdin). His appearances are rare and tied to specific FUN values.
• Mettaton’s quiz: In Hotland, you can answer his questions correctly to get a special interaction.
• Napstablook’s house: You can visit and get a special item.

Frequently Asked Questions

Can I do Pacifist after a Genocide run?

Yes, but the ending will be slightly altered (the “soulless” Pacifist ending) if you complete Genocide first. The game remembers your actions, and the final photo will show a creepy detail. A true reset (deleting the system files) can clear this, but the game warns against it.

What happens if I kill a monster by accident on Pacifist?

If you kill any monster, you are locked out of the Pacifist ending for that file. You can either continue to a Neutral ending or reset the game to start over. A normal reset is enough if you haven’t finished the game yet.

How do I spare Toriel?

In the fight, choose “Spare” repeatedly. She will eventually stop attacking and spare you. Do not use FIGHT at all, or you will kill her.

What is the hardest fight in Undertale?

Most players consider Sans (Genocide route) the hardest boss. His attacks are fast, and he uses a special mechanic that reduces your invincibility frames. Undyne the Undying is also very hard.

Can I get the Pacifist ending without befriending Undyne?

No. You must give Undyne water after her fight to befriend her. If you skip this, you cannot access the True Lab, and the Pacifist ending is locked.

Does fleeing count as sparing?

Fleeing is not the same as sparing, but it also doesn’t count as killing. Fleeing can help you avoid kills in a Neutral run, but for Pacifist, you must use the MERCY option to spare (or flee if the monster is not sparable, but this may lock you out of some interactions).

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