Undertale Yellow Guide: Walkthrough & Tips for New Players

The area order, every main boss, where to shop and how to survive your first run of Undertale Yellow — summarised from the developers' patch notes, the community wiki and our own play of the browser version. Light spoilers for area names and bosses only.

Checked against official sources: November 8, 2026

Pixel-art battle box: a yellow heart SOUL shooting at falling star bullets beside a circular aiming target

Before you start

Play UNDERTALE first if you can. The team says Undertale Yellow contains spoilers for the original and has a slightly higher difficulty.
Choose a difficulty. Since version 1.3 you pick it when starting a New Game. Easy Mode (hats give DEF) can also be toggled mid-playthrough.
Decide on a route early. Killing monsters or sparing them changes the story. See routes and endings before your first fight if you want a specific ending.
Save often. Flowey handles saving at the yellow save stars. In the browser version saves stay in your browser for this site.

Basic controls

Arrows
Walk / move SOUL

Z Enter
Confirm, attack, shoot

X
Cancel

C
Open the menu

Battle tips

Time the circular target. Attacks use a shrinking white ring: stop it close to the centre for more damage; if it reaches the centre you miss.
Read the ACT options. Every monster can be spared. When the name turns yellow, select MERCY → Spare. In version 1.1 the team even rewrote one of Sir Slither's ACT lines to make his spare condition clearer.
Check your food. Since 1.3, hovering a food item in battle shows how much HP it heals.
Fleeing is safe now. 1.3 guarantees a successful flee after two failed attempts, and you get a short break from random encounters after sparing or fleeing.
Use the helpers. Auto-Fire (togglable from the death screen of relevant fights) and Auto-Rhythm for the rhythm fight remove the most hand-straining parts.
Gold is easier in 1.3. Enemies drop about 30% more G to make up for the lower encounter rate, and the Delta Rune Patch now costs 80G.

Undertale Yellow walkthrough: areas in order

1. The Ruins & the Dark Ruins

Miniboss: Decibat · Boss: Dalv

Clover meets Toriel and walks the familiar Ruins until the switch room, where a switch Flowey tampered with drops them into the Dark Ruins — a darker, older lower level the original game never showed. Puzzles here use switches, glowing boxes and spike traps; one room's plaque literally reads "EXPOSITION". Every new monster of the area is fought down here, including the bat Decibat (the game's first miniboss, mirroring Napstablook) and the hooded recluse Dalv.

Clover in a corridor of the Dark Ruins, the purple lower layer of the Ruins — Dark Ruins — official screenshot

2. Snowdin

Boss: Martlet

A lower stretch of the snowy forest. Expect new monsters such as Frostermit, Insomnitot, Know Cone and Trihecta, a magma-and-ice puzzle where you guide a rolling rock to melt an ice cube three times, and the Honeydew Resort. Royal Guard recruit Martlet confronts Clover here; if her HP is depleted she retreats.

Clover walking through the snowy paths of Snowdin with a save star — Snowdin forest — official screenshot

3. The Dunes

Miniboss: El Bailador

After a trip toward Hotland goes wrong, Clover crash-lands in a desert lit by glowing Swelterstones. The Dunes contain the East Mines run by Mining Co., the town of Oasis Valley (Ceroba's house is just north of it) and the luchador-style El Bailador, fought at the end of the East Mines with a dance-mat mechanic.

Clover walking down a rope-lined path in the desert Dunes — The Dunes — official screenshot

4. The Wild East

Minibosses: the Feisty Four · Boss: Starlo

A cowboy town run by sheriff Starlo ("North Star") and his posse, the Feisty Five. Clover is put through a series of tests before the showdown with Starlo. Visit the saloon shop, the Hospital (the doctor can boost you 15 HP over your maximum) and Blackjack's — the only shop in the game where you can sell items. The stable hosts a card game called Six Shooter.

Clover standing between two monsters outside a building in the Wild East — Wild East — official screenshot

5. The Steamworks

Miniboss: Guardener · Boss: Axis

A decommissioned power plant that predates the CORE, full of old robots. Guardener guards the Greenhouse, and Axis — a guard robot built by Chujin Ketsukane — chases Clover through much of the facility. On Pacifist you travel with Ceroba; otherwise Flowey tags along. Carrying the Golden Pear, Golden Coffee and Golden Cactus unlocks the optional Macro Froggit fight on Pacifist and Neutral.

6. Hotland & New Home

Final boss depends on your route

An elevator links the Steamworks to Hotland's UG Apartments. This Hotland is set before Alphys and Mettaton changed it, and UGPS mail stations stand where the River Person would be. The story's final act plays out in New Home — who you face there depends on the choices you made.

Puzzles that trip people up

Dark Ruins switch room: three wall switches block the next room with spikes; the wiki's solution is to pull the third, then the first, then the second lever.
Chemistry mixing puzzle: since 1.3 you can pause it with the menu button (C, or Y on a controller), and the sequence slows down after you fail 7 times.
Minecart and steam puzzles: version 1.1 fixed crashes here (sending a cart off track, backtracking on the second steam puzzle). Play on 1.3.1 — the build on this site — to avoid them.

Mail and side content

The UGPS mail system lets past pals send Clover letters as the story moves on, and Hotland's UGPS stations stand where UNDERTALE's River Person would be. Other optional content includes the Honeydew Resort in Snowdin, the Six Shooter card game in the Wild East and the Macro Froggit fight in the Steamworks.

Undertale Yellow guide FAQ

What is the order of areas in Undertale Yellow?

The Ruins and the Dark Ruins, Snowdin, the Dunes (including the East Mines and Oasis Valley), the Wild East, the Steamworks, then Hotland and New Home for the finale.

Who are the bosses in Undertale Yellow?

Main bosses include Dalv (Dark Ruins), Martlet (Snowdin), Starlo (Wild East) and Axis (Steamworks). Minibosses include Decibat, El Bailador, the Feisty Four and Guardener. The final boss depends on your route: Ceroba on Pacifist, Flowey on Neutral.

How do I flee a battle in Undertale Yellow?

Use MERCY then Flee. Since version 1.3 fleeing is guaranteed after two failed attempts, and you will not run into another encounter immediately after sparing or fleeing.

Where can I sell items in Undertale Yellow?

Blackjack's shop in the Wild East is the only shop in the game where you can sell items.