UNDERTALE beginner guide: ACT, Spare, attack colors, healing and saves

Edition: UNDERTALE for PC (Steam), base game and normal mode. Based on Japanese display, with some English command names alongside. Excludes the demo, Hard Mode, console-exclusive content, 10th-anniversary-stream alterations and DELTARUNE

Verification scope: Official and guide sources checked on 2026-10-04. Gameplay and installed build number have not been tested. Historical values are not presented as verified on the latest installed build

Sources checked: 2026-10-04

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Check basic PC controls

Basic keyboard inputs are listed below. With controllers or remapped keys, follow the controls shown in your game.

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Check basic PC controls: 4 entries
Action	Basic keyboard input
Confirm or interact	Z
Cancel	X
Open menu	C
Toggle fullscreen	F4

Repeatedly advancing dialogue can skip enemy reactions and puzzle hints. Read an explanation at least once before moving on.

Set up conditions with ACT, then finish with MERCY

If avoiding kills, inspect ACT options first. Check descriptions can provide clues too
Try one interaction and check whether the next text changes
When the name has the sparing color, choose MERCY then Spare. Against groups, you can spare some enemies first to reduce their number
Even without a name-color change, some enemies are resolved through repeated Spare or Flee

Yellow is the usual indicator, but a Ruins conversation can change it to white or pink. A non-yellow name does not prove sparing is impossible. Weakening enemies can also work, but try ACT first if you want to avoid accidental kills.

Attack colors and heart colors follow different rules

Attack color affects what happens on contact; heart color affects how you move. Do not confuse light-blue attacks with a blue heart.

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Attack colors and heart colors follow different rules: 5 entries
What you see	Basic response
White attack	Avoid contact
Light-blue attack	Remain still as it passes
Orange attack	Keep moving during contact
Green attack	May heal or advance sparing conditions; not every green attack heals
A heart changed to blue, green, purple or yellow	Read that battle's controls. A blue heart introduces gravity and jumping

Red can indicate a warning, but red is not always harmless. Appearance alone does not establish a shared safe spot across every battle.

Choose one gap to move through next

When an attack begins, find a nearby gap from your current position
Move only as much as needed after seeing the bullets. Avoid moving back and forth in a safe spot
If cornered, create room to move before the next attack begins
After repeated losses, isolate one issue, such as failing to stop for light-blue attacks or jumping too high

This is general practice advice. Follow individual rules for attacks with changing safe positions or orange attacks requiring movement.

Distinguish save points, eight inventory slots and boxes

When HP is low, inspect a star-shaped save point. Healing there and recording with SAVE are separate actions
Your inventory has eight slots. Keeping one free makes receiving new items easier
Put items for later or old equipment into dimensional boxes available from Snowdin onward
Withdraw healing supplies before bosses. Check equipped gear and carried items separately

Each box has ten slots, and the same box's contents are available from other locations. Later phone functions still do not allow restocking during battle.

Secure early armor and healing options

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Secure early armor and healing options: 5 entries
Item or location	Use	Note
Ribbon armor found in the Ruins	An option to replace initial equipment	Equip it after collecting it
Manly Bandanna in Snowdin	Shop armor; normally 50G and +7 defense	Armor helps even when you avoid attacking
Bisicle in Snowdin	Restores 11 HP per use, with a remaining portion usable again	It does not restore both portions at once
Cloudy Glasses in Waterfall	Armor extending invulnerability after being hit	Compare extra effects as well as defense
The pie at Toriel's home	A full-HP recovery item you can keep for later	Keeping it is optional; using it early does not block normal progression

These examples help plan spending. Check prices and effects displayed in your game as well.

Answer 7 (spoilers)

Answer — reveal (spoilers)Close

Ruins enemies: open explicit sparing examples

The following are solutions for early encounters, with English command names.

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Ruins enemies: open explicit sparing examples: 5 entries
Opponent	Steps
Froggit	ACT: Compliment, then Spare
Whimsun / Moldsmal	You can try Spare immediately
Loox	Don't Pick On, then Spare
Vegetoid	Dinner, then collect green vegetables during the attack, then Spare
Migosp	Spare the other enemies first, then Spare this enemy when alone

If unsure, reduce the group by ending encounters you can resolve first rather than trying every ACT on everyone. This applies to the listed combinations, not every enemy.

Frequently asked questions

Does selecting an attack ruin a no-kill run?

Selecting an attack alone does not decide it. Check whether a kill granted EXP. If you killed accidentally but have not overwritten your save, reload the earlier SAVE.

Is using items during battle wasteful?

Healing is worthwhile if it lets you survive the next attack. You may prioritize reaching the next save over keeping an item unused.

Is Spare pointless unless the name is yellow?

Name-color settings and bosses requiring repeated Spare are exceptions. Check descriptions and battle changes as well.