How to Beat Undyne the Undying: Strategies for Undertale’s Toughest Battle

If you’re wondering how to beat Undyne the Undying in Undertale, you’re not alone. It’s one of the most demanding challenges the game has to offer. 

If you’re on the Genocide route, this remixed boss fight is unavoidable and tests your reflexes and mental stamina. Undyne’s determination turns her into a relentless opponent, and you have to adapt quickly if you want to survive. 

This guide will walk you through how to beat Undyne the Undying with strategies gathered from personal experience and community wisdom. I’ll cover preparation, attack patterns and resource management so you can progress through the Underground with confidence.

How to Beat Undyne the Undying: Preparing for the Fight

Before the first spear is thrown, it pays to prepare. Undyne is one of the strongest bosses in the game and fighting her is required to advance. She also fights differently on the Genocide route, so leveling up and equipping the right gear can make a huge difference. 

I recommend visiting shops in Snowdin and Waterfall to buy healing items like Crab Apples, Sea Tea and Glamburgers. Items with invincibility frames such as Cloudy Glasses allow you to take a hit and have a brief window of safety.

Gear matters too. The Ballet Shoes weapon gives you three attack bars, and hitting all bars precisely yields high damage. Pair it with the Stained Apron or Cloudy Glasses for additional defense or invincibility frames. When you initiate the fight, be aware that she will immediately turn your soul green and begin throwing arrows. 

You’ll need to move a shield in the direction of incoming arrows, so consider playing Undertale in full screen for better visibility. Our guide on how to fullscreen Undertale describes how to toggle windowed and full‑screen modes using F4 or Alt + Enter. Having a clear view of the battle box helps you respond to fast arrows and flip arrows that change direction mid‑flight.

It’s also worth practicing the standard Undyne fight on a Neutral save before attempting the Genocide version. The neutral encounter familiarizes you with the rhythm of arrow attacks and the switches between green and red soul phases. This practice run helps build muscle memory so that, when the battle escalates, you’re ready to react instinctively.

Mastering Undyne’s Attack Patterns

Undyne the Undying mixes set patterns with unpredictable barrages, so recognizing each type of attack is vital. During the opening green soul phase, she will send waves of arrows from multiple directions. Slow arrows give you time to reposition your shield, while fast arrows require quick reactions. Flip arrows change direction as they approach, so wait until they flip before blocking.

Once Undyne switches your soul back to red, she peppers the arena with spears that travel toward you. Many of these attacks rely on memorization. For the slow arrows attack, focus on your soul rather than the individual arrows; this makes it easier to see which arrows are closest. When you’re surrounded by random spears in red soul mode, move in a circular motion to dodge. Staying near the edges of the box reduces the number of directions from which spears can reach you.

Undyne also employs several random patterns that can catch you off guard. In the small‑box attack, spears rise from below. The best tactic is to stay near the top of the box and occupy only one third of the space; as soon as a spear appears beneath you, move to another third. There’s also a pattern where spears close in from both sides. Holding the run button (B) and sliding toward the left wall before moving up allows you to squeeze through. Finally, she may throw sets of six spears; here again, moving in a circle and keeping a consistent rhythm helps you avoid them. Don’t panic if you take a few hits during these random attacks; remember that each pattern repeats, so surviving once makes the next round easier.

When your soul returns to green, be ready for increasingly fast flip arrows. Blocking them becomes a matter of anticipation rather than reaction. Many players find it helpful to count the arrows and move the shield pre‑emptively. Between waves, prepare your offensive strikes: time your Ballet Shoes bars carefully and focus on landing all three hits.

Offensive Tactics and Resource Management

Knowing how to beat Undyne the Undying isn’t only about defense. You must also dish out enough damage to deplete her massive health pool. On the Genocide route, the battle begins after you defeat Monster Kid, and Undyne takes the hit for them. She rises again with determination, her name changing to “Undyne the Undying” and her attacks becoming faster and more powerful. During this phase, each of her attacks deals eight to twelve damage, so maintaining high HP is essential.

Attack whenever you have a clear opening. Use the Ballet Shoes to maximize damage, and don’t rush the timing bars. It’s tempting to mash the fight button after each wave, but a mistimed hit wastes your turn and forces you to defend longer. If you struggle to land all three bars, practice outside the boss fight or consider equipping a different weapon with a single timing bar.

Healing management is equally important. In my own playthroughs, I carried at least six healing items, prioritizing those that restore 14 HP or more. Use recovery items when your health drops below half, but avoid eating rare items like Butterscotch Pie, which can help in later fights. Instant Noodles heal you fully but take longer to consume, so use them when you need a breather. 

Sea Tea temporarily increases your movement speed, which can help during fast arrow phases. Remember that if you die, you keep any unused items, so it’s better to eat something than to fall with a full inventory.

Building Determination and Practicing Persistence

Undyne the Undying embodies the theme of determination, and so must you. The unique combat system that combines bullet‑hell dodging with turn‑based attacks is part of what makes Undertale so special. 

The game’s memorable characters and fourth‑wall‑breaking story raised the bar for the RPG genre, and this fight is a highlight of that design. If you feel overwhelmed, take a break and come back with a clear head. Repetition builds muscle memory; the more you face her patterns, the less intimidating they become.

Choosing to pursue the Genocide route also means embracing the consequences. Your actions shape the story and determine how characters respond to you. Undertale’s freedom to spare or kill every enemy is why it’s considered a masterpiece. 

If you decide the Genocide route isn’t for you, fleeing during the red soul phase allows you to escape and continue on a Neutral path. That choice leads to a completely different ending, and exploring these possibilities is part of what makes games with multiple endings so engaging.

Once you’ve beaten Undyne the Undying or experienced one of Undertale’s other routes, you might be looking for similar adventures. Our overview of games like Undertale celebrates indie titles with innovative storytelling and emotional depth. 

Finishing the Fight and Moving Forward

As Undyne’s health diminishes, her attacks slow down. Keep your focus and continue the rhythm of block, dodge, and strike. Eventually, she will yield, acknowledging your strength before fading away. 

Defeating her clears the path to Hotland and sets the stage for even harder battles. The sense of accomplishment from overcoming this fight is immense; you have proven your determination. If you haven’t played the game, pick up our Undertale Steam key from the Eneba marketplace. The game’s bullet‑hell encounters and multiple endings provide endless replay value, and owning a digital copy ensures you can revisit the Underground whenever you want. 

With the right preparation and a little perseverance, you’ll not only learn how to beat Undyne the Undying but also appreciate why this indie RPG continues to inspire players around the world.

FAQs

What level should I be to beat Undyne the Undying in Undertale?

To beat Undyne the Undying in Undertale, you should aim to reach at least LV 10 on the Genocide route. Most players arrive at this fight with around 92 HP, which provides enough health to survive her eight‑ to twelve‑damage attacks. Level isn’t everything, however, and proper dodging and healing are more important than raw stats.

How much HP does Undyne the Undying have?

Undyne the Undying has a significantly larger health pool than her normal form; the fight ends only after depleting tens of thousands of HP through repeated attacks. Because her attacks slow down near the end, persistence and patience will see you through.

What is the easiest way to defeat Undyne the Undying?

The easiest way to defeat Undyne the Undying is to memorize her attack patterns and manage your healing items carefully. Focus on your soul rather than individual arrows, move in circles during spear storms, and attack deliberately with the Ballet Shoes.

Why is Undyne the Undying so hard?

Undyne the Undying is so hard because she combines fast, random bullet‑hell attacks with a huge health pool and increased damage. Her determination in the Genocide route also means she fights longer and with more varied patterns than in other routes.

Can you avoid fighting Undyne the Undying?

Yes, you can avoid fighting Undyne the Undying by choosing not to continue the Genocide route. If you spare Monster Kid and flee during the red soul phases, the encounter ends, and you switch to the Neutral route. This decision leads to a different story outcome and lets you bypass the hardest version of the fight.