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Undertale Yellow is a stunning game that offers mystical adventures in the Underground. To win boss combats, you must attack bosses while protecting the Soul.


Do you know what is the inspiration for this game? Undertale is the answer. It is a great indie game developed by Toby Fox. This game takes you on an extraordinary journey through a rich and vibrant world unlike any other. With its captivating storytelling, unique characters, and innovative gameplay mechanics, this game has captured the hearts of players worldwide. Combining elements of role-playing, exploration, and moral choices, the game challenges players to navigate a realm inhabited by monsters and humans, where every decision has consequences. The game's emphasis on player agency, its thought-provoking themes, and its memorable soundtrack have established it as a beloved and influential title in the realm of video games, offering an unforgettable experience that transcends traditional gaming conventions.

Relevant information about Undertale Yellow

The release of the game

Hot on the heels of the success of Undertale, a new fan-made game was released. It is Undertale Yellow which was created by GameMaker: Studio. On November 30, 2016, the creator launched a demo. This demo quickly attracted many players from all over the world. After recognizing the popularity of this game, the developer decided to release the complete game on December 9, 2023. Its release has swiftly taken the internet by storm and captivated many YouTubers, streamers, and players. It is possible to say that this challenging action game ignites a fresh trend in the online gaming community.

The secret story behind the game

Although this game is considered to be a prequel to Undertale, its story is not too different from the original version. This game is also about the war between humans and monsters. Moreover, when joining this game, you will follow the steps of the seventh human named Clover. She is a young child who wants to explore the Underground. She does not care about the rumors about the disappearances of travelers visiting Mount Ebott. Both Clover and Flowey head toward Mount Ebott and enter the Underground. In the Underground, they encounter many dangerous monsters sealed underground. Then, the battles between them start and you need to save Clover from the monsters.

Engaging gameplay of Undertale Yellow

An exciting adventure

This game will take you on a wonderful adventure in which you can explore the Underground. You will start from the Ruins. Then, you will go to different places. In these places, you will meet different people who assist you a lot. Here are some suggested locations you can visit.

  • Dunes: This is a large desert that is scorched and arid. Although this region has many minerals and other important materials, it also hides many monsters.
  • Steamworks: This is a decommissioned factory that is full of old robots. When visiting this factory, you will encounter Axis Model 014.
  • Snowdin: This is a large snowy region that is located right after the Ruins. This region has more bosses than other regions. You need to join the battles with 4 bosses who are Frostermit, Insomnitot, Know Cone, and Trihecta.
  • Wild East: This is a town that is famous for a shop named Blackjack. In this shop, you can sell your items such as weapons and minerals.
  • Hotland: If you want to leave the Underground and return to the Undertale, you need to find Hotland. There is no boss in this room, so you do not worry when visiting it.

Thrilling boss fights

When visiting different places, you will encounter different bosses. You need to embark on the fights against them and try your best to defeat them. At the start of the fight, a target board will appear and a white ring will move from the outside of the target and quickly move inward. When the circle gets closer to the middle, you need to press a Z key to attack the boss. The power of your attack depends on the distance between the white ring and the center of the target board. After this attack, it's your opponent's turn. Your rival will attack you constantly, so you need to control your soul to move around to evade these attacks. Pay attention to your blood bar at the bottom of the screen. If it is empty, your soul heart will break and the game is over. However, do not give up and press the restart button to join the battle again.

Useful items

Before starting the battles with bosses in this game, I advise you to purchase items first. This game introduces an array of intriguing items.

  • Hot Pop: This item serves as a consumable resource with a distinct effect. When used, it replenishes 14 health points, rejuvenating you in the midst of intense battles or challenging situations.
  • Cold Pop: Contrasting the Hot Pop, this item offers a refreshing twist. It also restores your health, but it also grants a temporary boost to your agility and speed.
  • Warm Pop: This item embodies a balance between the Hot and Cold Pops. When consumed, it restores a moderate amount of health while also providing a subtle increase in the protagonist's defense.
  • Honeydew Coffee: When you buy this item, it grants you additional turns or actions, allowing for increased strategic flexibility during battles.
  • Coffee Beans: This item possesses a unique function. When used during battles, they replenish your health to a lesser extent compared to the Hot, Cold, or Warm Pops. However, Coffee Beans have an additional chance of triggering special effects, such as temporary invincibility, increased attack power, or unique abilities, adding an element of unpredictability and excitement to combat encounters.
  • Corn Dog: This item serves as a hearty snack that replenishes your health because it helps to increase 12 health points.
  • Candy Corn: This item provides 9 health points, subtly increasing your overall resilience.

How to control

Press the Z or X key to continue the game or choose.

Press the arrow keys to guide the soul to move around the playing field.

New characters in Undertale Yellow

Besides old characters, this new version introduces several new characters that add depth and intrigue to the game's story.

  • Zenith Martlet: Zenith Martlet serves as one of the significant adversaries in the game. This character presents formidable challenges and unique battle mechanics for players to overcome during their journey. Defeating Zenith Martlet requires strategic thinking and adaptability.
  • Axis: Axis is a visually striking robot characterized by its gray metallic exterior and distinct features. His large box-shaped head houses two pink, unevenly sized eyes and a horizontal line of bolts or holes that resemble a mouth. During the intense battle with Axis, you control the Soul and must utilize a unique mechanic involving a trashcan lid. Axis equips Clover with this lid, considering it a threat. The lid serves as a shield, enabling Clover to block Axis's attacks effectively.
  • Starlo: This is a humanoid monster exuding an aura of authority and confidence. During the battle with Starlo, you can control the Soul move within a small radius. The challenge lies in dodging Starlo's various attacks while navigating this limited range of movement.

The hardest boss in Undertale Yellow

When speaking about the most difficult boss in this game, Marlet is the first name in the boss ranking tier. This boss appears at the Genocide Route in the Snowdin. As a member of the Underground Royal Guard, Marlet is really powerful.

The fight against Marlet has three phases. In the battle, you will encounter her constant attacks. First, she will use her feathers to attack you. You need to move the Soul around the playing field to dodge the feathers. After the feather attack, the packages will be thrown at you. Let's guide the Soul to move to the left or right to evade the packages. Then, the feathers reappear, but now they circle you. These feathers move slowly toward the target and then explode into 3 or 4 smaller feathers. Next, the bigger feathers emerge and move in a spiral pattern. If you can avoid all feathers and survive, you will need to confront the tornado attack. The random items drop from the top and then disappear when they reach the bottom. Be quick to take control of the Soul to move from left to right and vice versa. Ultimately, the feathers appear one more time and circle the Bullet Board. You should be careful with these feathers and try to stay alive until the end of the fight.

Effective tips to defeat Marlet

Because the battle with Marlet is super difficult, I will suggest some effective tips. By following these tips and strategies, you can enhance your chances of winning the game

Phase 1 Tips

  • Utilize Silver Bullets and Glass Ammo: Silver Bullets deal 79 damage, while Glass Ammo can be used for healing or dealing damage. Experiment with both to find the most effective approach for your play style.
  • Obtain Auto-Fire: To make the battle easier to manage, intentionally "die" at the beginning of the fight to grab the auto-fire option. This will allow you to focus more on dodging attacks.
  • Take Advantage of Time Stops: Before the first glass blocks form to introduce dashing, hold down a charge shot. This enables you to shoot Zenith Martlet during the time stop, dealing free damage.
  • Diagonal Dodging: Dodging feathers can be made easier by moving diagonally. This provides better maneuverability and increases your chances of avoiding incoming attacks.
  • Feather Storm: During the yellow feather storm attack, drag charge shots across the screen while continuing to dodge diagonally. This strategy can help you manage the onslaught of feathers more effectively.
  • Positioning during Item Drops: Stay off the bottom of the screen and spam the dash command while maintaining a central position. This approach can help you evade the challenging item drop spam attacks.
  • Recognize Claw Attack Patterns: The claws have the same attack pattern in the combos they appear in. Pay attention to their movements and attack sequences to anticipate and dodge effectively.
  • Timing Heals: Avoid using heals just before Phase 2 begins. You will receive a full heal once Phase 2 starts, and using a heal action before that point would be redundant. Instead, save your healing items for Phase 2.

Phase 2 Tips

  • Strategic Decision-making: Only attack if your HP is high. If your HP is low, use the Endure ACT instead. You can compensate for lower DPS by employing the Soul-Shot.
  • Dealing with Yellow Rocks: You only need to break one of the two chunks of yellow rocks to negate the damage entirely. Remember that the rocks spawn in the same place every time.
  • Navigating the Stars: Fully destroy the first star with charge shots, then split the remaining stars into two or more pieces. Drag them across the box, creating more manageable patterns to dodge.
  • Breaking Glass Boxes: Dash into the wall to break the glass boxes. It doesn't matter if you're up against it, as long as you hold a movement key, you're fine.
  • Feather and Meteor Shower Combination: Focus on the rocks during this attack since they are slower and will hit you just after your invincibility frames end. Feathers can be dodged or tanked since they move quickly.
  • Dealing with Golden Wings: Use charge shots and dash towards the wall they appear in to dodge the feathers. Alternatively, position yourself near the bottom and make slight movements to navigate between the feathers. Be aware that additional feathers will attack in the same spots during Phase 2.
  • Understand the Win Condition: Note that you cannot defeat Zenith Martlet with Soul-Shot. The only way to achieve victory is through regular attacks. However, you can bring her down to 1 HP, at which point Soul attacks will deal no damage.


In conclusion, it is possible to say that Undertale Yellow is the most successful fan-made game inspired by the beloved original Undertale, and offers you a captivating and immersive experience. The story presented in this game is engaging and thought-provoking. In terms of gameplay mechanics, this game introduces innovative features that enhance the overall experience. The incorporation of new battle mechanics, such as the use of Silver Bullets and Glass Ammo, adds depth and strategy to the encounters. The game's unique phase-based battles, like the intense showdown with Zenith Martlet, require players to adapt their tactics and utilize specific strategies to emerge victorious. These additions provide a fresh spin on the familiar Undertale formula, ensuring an engaging and challenging gameplay experience. Therefore, try this game now or add it to your game inventory!