Undertale: Complete Guide

A route-by-route guide to Undertale: how the battle system works, how to get the Neutral, True Pacifist and Genocide endings, boss tips for every major fight, and the secrets people usually miss.

Researched September 2026 — current as of PC version 1.08 (December 2017; the game has been stable since). Live games change; check the linked sources if something differs.

Spoiler warning: this guide names bosses and ending requirements.

Quick Start

1. You never have to kill anyone. Every enemy can be spared by using ACT until their name turns yellow, then choosing MERCY, then Spare.
2. Play blind first if you can. Undertale's best moments rely on surprise. Come back to this guide when stuck.
3. Your first ending is a Neutral ending. True Pacifist requires finishing a Neutral run with zero kills, then reloading your save.
4. The game remembers. Resetting or reloading doesn't erase everything - characters comment on what you did in earlier attempts.
5. Blue attacks: stand still. Orange attacks: keep moving. This rule saves a lot of HP.
6. Save at every star. Save points also fully heal you.
7. Carry healing items. Buy cheap consumables in each town; Snowdin and Hotland shops are the main stops.
8. Controls: Z (or Enter) confirms, X (or Shift) cancels, C (or Ctrl) opens the menu, arrow keys move. F4 toggles fullscreen; hold Esc to quit.
9. There are no Steam achievements for Undertale - completion is about endings, dog counting, and secrets.

How Battles Work

Each turn you choose from four buttons:

Then the enemy attacks, and you control your SOUL (a heart) inside a box, dodging bullets like a shoot-'em-up.

SOUL modes

Stats

• LV (LOVE) and EXP go up only when you kill. At LV 1 you're weaker but defense and attack items make up for it.
• HP rises with LV, so pacifist runs rely more on items and dodging skill.
• Check enemies with ACT - it shows their stats and a hint about how to spare them.

Routes and Endings

True Pacifist requirements

1. Finish a Neutral run without gaining any EXP. Sparing Flowey at the end is recommended - he gives you hints about what to do next - but killing him grants no EXP and doesn't fail the route.
2. Reload your save (you'll be before the final area).
3. Papyrus's hangout in Snowdin (spare him and go on his date).
4. Undyne's hangout at her house in Waterfall - you need to spare her in Hotland first by giving her water from the water cooler when she collapses.
5. Deliver Undyne's Letter to Alphys, then Alphys's date at the garbage dump.
6. Return to Alphys's Lab when Papyrus calls - follow Alphys's note to the "bathroom" door; the elevator behind it takes you to the True Lab. Explore it fully.
7. Face the final boss and use the SAVE mechanic to reach your friends.

What doesn't break the route: attacking without killing, killing the Dummy in the Ruins, and the Asgore/Flowey outcomes at the end of Neutral (none grant EXP). Attacking Mad Mew Mew when she can be spared also doesn't abort it, though sparing her is the nicer outcome.

Genocide requirements

• In each area, keep fighting random encounters and killing everything until the game says "But nobody came."
• Check the kill counter by opening a save point - if it shows a number, you haven't cleared the area.
• Missing a single required kill quietly drops you onto a Neutral route.
• Genocide unlocks unique encounters, including one of the most notorious boss fights in indie games.
• Genocide permanently affects future True Pacifist endings in that install. Think carefully before doing it.

Area Walkthrough and Boss Tips

The Ruins

• Flowey introduces the "friendliness pellets." Don't touch them.
• Napstablook: keep using Cheer until they leave happily.
• Toriel: keep choosing Spare repeatedly - it seems to do nothing, but after several turns the fight ends peacefully. Her attacks avoid you if your HP is low.
• Items: Toy Knife and Faded Ribbon are in the Ruins; the Spider Bake Sale sells the Spider Donut and Spider Cider (buying something helps against Muffet later).
• Answer Toriel's pie question however you like; it only changes flavor.

Snowdin

• The dogs: Doggo (don't move when he's looking), Lesser Dog (pet repeatedly), Dogamy and Dogaressa (roll around, then pet), Greater Dog (call it, then pet and play).
• Papyrus: use Spare or Flirt; survive his blue attacks by standing still, and his gravity phase by jumping. At the end, he offers his friendship.
• Shop: buy the Tough Glove and Manly Bandanna if you're not pacifist, or healing items for a pacifist run.
• Sans appears throughout; his phone number and later interactions matter for some Neutral endings.

Waterfall

• Shyren: hum and help her sing.
• Mad Dummy: stand so its knife and missiles hit the dummy itself.
• Undyne chases you through Waterfall. In the fight, the green SOUL shield blocks arrows; later, flee downward to escape into Hotland.
• Temmie Village: buy Temmie Flakes and the Temmie Armor (expensive, but price drops the more you die). You can also pay for Temmie's college.
• Ballet Shoes, Old Tutu and Cloudy Glasses are all found in Waterfall.

Hotland and the CORE

• Alphys and Mettaton drive most of Hotland's story beats: the quiz show, cooking show, news report and puzzles.
• Royal Guards 01 and 02: use their ACT options (such as Clean Armor and Whisper) until they open up to each other - then they walk off.
• Muffet: buying from the Spider Bake Sale makes the fight easier; you can also pay her off. Her pet spider phase moves the web; keep to a lane and time jumps between lines.
• Mettaton EX: use Pose, Boast, Heal on camera and dodging well to push the ratings up. At 10,000 ratings he ends the show early.
• Bratty and Catty sell the Empty Gun; the Burnt Pan and Stained Apron are also in Hotland.
• The CORE is a maze; follow the signage and use save points.

New Home

• Read the dialogue in Asgore's home; it tells the full backstory.
• Worn Dagger and Heart Locket are found here - the strongest normal gear.
• Asgore: you can't spare him directly; defeat him. On a Neutral route, Flowey intervenes.
• Omega Flowey (Photoshop Flowey): dodge through each phase and use ACT when prompted to call for help - the human SOULs assist you. Saves happen automatically during the fight, so a death isn't a full restart.

Gear Summary

Temmie Armor (Temmie Village) is the strongest armor you can buy in a non-Genocide run.

Secrets and Missables

• Dog Shrine: donate gold in Waterfall to upgrade a small shrine.
• The Mysterious Door and the Gaster Followers appear only with certain "fun" values - randomized and rare.
• Hard Mode: name yourself "Frisk" at the naming screen.
• Some names trigger special responses at the naming screen.
• Nice Cream in Snowdin and Waterfall comes with punch cards you can redeem.
• The entries and tapes in the True Lab are key lore - read and watch everything on True Pacifist.
• Toriel's phone calls in the Ruins change based on your actions.
• Sans and Grillby's: talk to Sans in Snowdin and take him up on his offers - his dialogue changes across routes.

Common Mistakes to Avoid

1. Killing a single monster "by accident" on a pacifist run. One kill locks True Pacifist until you replay. Use the Check ACT to learn how to spare.
2. Not sparing Flowey at the end of Neutral. It isn't strictly required, but sparing him gets you his hints about how to reach True Pacifist.
3. Skipping Undyne's water in Hotland. Without it, you can't get her hangout.
4. Leaving the True Lab early. Explore it all to finish the story.
5. Moving during blue attacks. Stand still and they pass through.
6. Doing Genocide casually. It changes your future True Pacifist ending in that install.

Advanced Tips

• Crit timing: stopping the FIGHT bar exactly in the center gives bonus damage - useful on Neutral runs.
• Use items mid-fight wisely: healing items take a turn; the Butterscotch Pie from Toriel fully heals.
• Defense matters on pacifist runs: Temmie Armor, Cloudy Glasses and Heart Locket help with invincibility frames and damage reduction.
• Mettaton EX: save your best dodges for the camera-heavy phases, and use items when it says "heal" for bonus ratings.
• Genocide Sans: learn the attack patterns in order; the fight is pure memorization, so stock your best healing items and expect many attempts.
• Undoing Genocide means manually deleting the game's save and system files (with Steam Cloud turned off so they don't come back). Treat it as a one-way choice.

FAQ

How long is Undertale? Roughly 6-7 hours for a first Neutral run; True Pacifist adds a couple more hours.

Can I get True Pacifist on my first run? No. You must finish a Neutral route first, then reload your save to unlock the final steps.

Does killing Toriel or Papyrus ruin my run? It locks you out of True Pacifist for that playthrough, but you still get a Neutral ending.

Is Genocide worth doing? Many players prefer to watch it online. It's intentionally uncomfortable and permanently changes future Pacifist endings.

How many dogs are there? The store page joke asks you to count. The main dog encounters include the Annoying Dog, Doggo, Lesser Dog, Greater Dog, and Dogamy and Dogaressa - plus the Dog Shrine and many dog cameos.

Is Deltarune a sequel? Deltarune is a separate game by Toby Fox set in a different world with familiar characters. Undertale stands alone.

The game won't launch after a Steam client update - what now? The developer's 2016 note recommends opting out of the Steam client beta; you can also switch Undertale to the old_version_100 beta branch in Properties if the latest version misbehaves.

Sources

• Undertale on Steam
• Steam news: UNDERTALE Updated / Steam Client Beta Issues
• Undertale Wiki - True Pacifist Route
• Undertale Wiki - Version history