Top 10 Hardest Undertale Bosses

The Top Ten
1 Sans Sans or Sans the Skeleton is a character in the 2015 RPG Undertale created by Toby Fox. He is a lazy, pun-loving skeleton who is a supporting protagonist in the "pacifist" and "neutral" routes of Undertale, and a heroic antagonist/final boss of the "genocide" route. He is known for his incredibly difficult... read more

I couldn't get past the final Gaster Blaster circle for so long. Weeks after my first attempt on the computer (and maybe 57th), I downloaded it on my Switch, and the controls are so much better. The third bone stab (where he flings you into a random wall in the box and bones try to stab you) was almost impossible to get past undamaged.

I hated constantly being hit by those final Gaster Blasters. His fight was by far the hardest in the game. This makes Undyne the Undying look like a pushover. So yeah, I ended up having a very bad time.

2 Undyne The Undying Undyne is a main character in Toby Fox's 2015 RPG, Undertale. She is the heroic fishlike captain of the Royal Guard, who takes it upon herself to protect the monsters of the Underground. Her name is derived from the word "Undine", and is a pun on the word "Undying". Her most loved monsters are her mentor,... read more

I have been stuck on this fight since the start of December. The time I am posting this is December 22, which is 22 days. The farthest I have ever seen is 75 percent health. One of the first attacks has slow arrows. It seems like it's easy, but it's not because there are so many of them.

I beat every boss in Undertale within 4 or 5 tries. This is all except for Undyne the Undying (who I have been stuck on for weeks) and Sans (who I haven't fought because I'm stuck on Undyne the Undying). Omega Flowey took me about 3 tries and was a really quick boss fight because I'm pretty sure you don't have to repeat phases.

Asriel shouldn't be on this list because you can't die to him. Asgore was the hardest boss in all of the neutral/pacifist route (took me 5 tries). However, he does not even compare to the difficulty of Undyne the Undying. She should be second on this list.

3 Asriel Dreemurr Asriel Dreemurr is a character from the 2015 game Undertale. He was created by Toby Fox.

Asriel is the child of King Asgore Dreemurr and Queen Toriel, but he seemingly passed away prior to the game's events. His backstory is only focused on in the True Pacifist Route, which means the player does... read more

You can't fully die and don't have to restart the entire fight? Nice! So I will dodge attacks and die a couple of times. That's okay and will win, right? Easy boss! Well, that dodging isn't really, you know, and at 20 HP... Anyway, can't 'die' doesn't mean it's easy. Dodging the attacks is a huge challenge.

While you cannot die in this fight, his attacks are immensely hard to dodge and much more difficult than Omega Flowey's. The setback is really annoying as well because the chaos buster almost always decimates your health.

4 Omega Flowey

Although his battle does save, no amount of skill can let you not die on this guy. To be fair, I haven't attempted the genocide route, so I haven't battled Undyne the Undying or Sans, but he is much harder than Asriel, as his battle saves even more.

I died like 15 times on this fight. The main things that got me are the finger guns and the flies. Unavoidable. Anyway, this boss proves that Flowey is the best character, and nothing will ever beat him.

Looks like the hardest boss ever (tied with Sans) because it's so powerful. Imagine a talking, attacking, deadly flies-swinging cactus hands and shooting barrages of seeds all at once. Well, good luck on that one because it's pretty damn hard.

5 Asgore Asgore Dreemurr is a boss monster and the king of the monsters in the 2015 RPG Undertale made by Toby Fox. Asgore is the portrayed main antagonist who plans to acquire seven human souls and use their power to break the barrier that seals the monsters underground . Aspects of his character are hinted... read more

The first time I fought Asgore, I died to him at least 7 times. I just couldn't keep up with the attacks getting faster later on in the fight.

One of the hardest bosses. Worn Dagger is the strongest in this route, but Burnt Pan is the best. It can do 300 or more damage with a perfect hit.

Asgore was pretty hard, to be honest. But his attacks are decently easy to dodge once you learn them, especially the orange/blue axe attack (whatever you'd call it). It took me like 7 tries to beat him. This was pacifist, mind you.

6 Muffet Muffet is a character from the game Undertale. She appears in a region called Hotland, selling pastries to raise money to rent a heated limo to help the spider clan from the Ruins (who are also raising a bake sale) reunite with the one in Hotland because the spiders can't cross Snowdin.

Muffet got my vote. The way her attacks come at you... Eat a spider donut in front of her to skip the battle, or if you already bought a spider donut in the ruins, in the dinner phase, a spider will bring up a note and the battle will end. Struggle or pay to slow her attacks. Took me many tries.

Muffet is my fave character and super evil and cute. I mean, she can also control your soul like Sans, and every time I see the doughnuts and pastries, I get hungrier, which breaks my concentration.

Muffet is actually pretty easy to beat if you saved the spider donut or spider cider. I had it and ate it in front of her. But if you don't have one, you have to spare her 17 times, I think.

7 Mettaton Mettaton is a character in the popular 2015 RPG game, Undertale. He is a robot with a soul built by Dr. Alphys, and is the sole television star of the underground. Mettaton is a popular character in the fanbase. His notable features include his legs, and his catchphrase "OH YESSSS!"

Mettaton is the hardest pacifist fight, in my opinion. His attacks are super chaotic and almost impossible to dodge. Some may say Asgore is harder, but once you get his attacks, he's super easy. It took me 8 items to beat Mettaton and only 5 for Asgore. I died 3 times for both but barely beat Mettaton with 2 health, whereas I beat Asgore handily.

The reason why Mettaton is harder than Flowey or Asriel is because you can't lose to them. Anyway, Mettaton is epic.

I think I struggled with this boss fight the most. The bullet shooting is very unique and kinda hard, in my opinion. Probably the hardest boss fight in the game. I know about Sans, but after a bit of experience and learning his attacks, you don't struggle much against him, at least for me. Mettaton EX is hard, if not the hardest.

8 Undyne Undyne is a main character in Toby Fox's 2015 RPG, Undertale. She is the heroic fishlike captain of the Royal Guard, who takes it upon herself to protect the monsters of the Underground. Her name is derived from the word "Undine", and is a pun on the word "Undying". Her most loved monsters are her mentor,... read more

Waterfall is peaceful without Undyne and Mad Dummy. It should be noted there's a way to skip part of the battle if you get low HP, or even better if you use a skip with a healing item. This skip is not a glitch, by the way.

I had no problems with beating Undyne. She is difficult but fun at the same time, requiring exact timing and being able to move your shield to the right spot.

I struggled when fighting her. It took me about 7 tries. This should be swapped with Mettaton as number 6, with Mettaton at number 7.

9 Papyrus Papyrus is a character from the 2015 game Undertale, made by Toby Fox. He is the Younger brother of Sans the skeleton, royal guard in training, and a sentry in the town of Snowdin. Opposite to his brother, papyrus is active, loud, and full of himself; but in an endearing way. Papyrus means to become... read more

The only time I had trouble with Papyrus was when I was attempting the pacifist route.

He was only threatening in Disbelief. In regular Undertale, he is a cakewalk.

Slightly harder than Toriel, but still, you can't die, so it's easy.

10 Toriel Toriel is a goat like monster who is the secondary major character in Toby Fox's 2016 RPG, Undertale. She saves the protagonist from Flowey and guides them through the Ruins, of which she is the self-proclaimed caretaker. She is the ex-wife of Asgore, the mother of Asriel Dreemurr, the adoptive mother... read more

Toriel is possibly the easiest fight in the game, whether you're going pacifist, neutral, or genocide. You cannot die in this fight unless you intentionally run into the fire.

Technically, you can't die in this fight, but just try to not get to 2 HP when you are on pacifist. It's freaking impossible!

Strangely, I defeated Photoshop Flowey in three tries, but on my second playthrough, this was hard.

The Contenders
11 Mad Dummy

Waterfall is peaceful without Mad Dummy and Undyne. There's a way to win this in five turns, but this requires certain moves on the enemy turn.

It took me many tries. I just couldn't lead the projectiles to the dummy without getting hit myself.

He took me around 4 or 5 tries to beat, so not really that hard.

12 Disbelief Papyrus

Bones. Orange bones, blue bones, orange Gaster blasters, Sans, and Undyne the Undying.

13 Annoying Dog

This is actually most likely the strongest character in the game. He created this world (Undertale), so he can easily destroy it all. He could kill you (Frisk), Sans, Papyrus, Undyne, just with a single button.

By Derpo

Hardest boss ever! Who else agrees?

14 W.D. Gaster
15 Chara Chara is a character in the game Undertale by Toby "Radiation" Fox who is one of the seven people to fall to the Underground prior to the fall of the player character. Their name can be changed by the player and will be assumed as the player character, until the Pacifist Route when Asriel asks for the... read more

Okay, I know you never fight Chara in Undertale, but you see her in the genocide route. She one-hits you in the end before you even get your turn.

Oh jeez, this has to be the hardest. Most people don't know how to battle Chara. Look it up on YouTube and watch. Most are fake actually or fan-made. Trust me, harder than Sans.

Chara is a god. She can kill you so quickly.

16 Ultra Sans

He is awesome, and he is so hard. If you think Sans is hard, try this dude.

17 Frisk

Frisk is easily the hardest boss in the entire game. You can't even hit them. Why did Toby Fox put an unbeatable boss in the game?

Frisk can reset over and over. She is invincible. And she is you.

18 Temmie Temmie is minor character from the 2015 game Undertale made by Toby Fox. Made in the likeness of her artist, Temmie Chang, in appearance and character. Both a character and a species of monster, temmies are defined by their mix of cat and dog features, as well as their broken English. Their hidden village... read more
19 Froggit

Froggit didn't understand what you said but was flattered anyway.

Hardcore. I was stuck on them for a very long time. He wouldn't turn yellow, and I was so confused.

Just a normal Froggit, but it took me 26 tries. Is this Froggit a hacker, or am I glitched?

20 Mettaton NEO

Basically Undyne the Undying's fight.

21 Dusttale Sans

He has freaking more determination than you in the fan game.

22 Omega Flowey Flowey is a flower in the RPG Undertale. He is the first character you meet, and also your best friend.

He almost instakills you with a single hit, manipulates you, and makes it impossible to escape. By sheer luck, they make a mistake and use a super heal on you, which they could easily use on themselves! You also don't even have the option to act! They just have one attack, and they go first instead of you. Plus, they will remember everything!

23 Alphys NEO
24 Napstablook Napstablook is a secondary character from Toby Fox's 2016 RPG, Undertale. He is the cousin of Mettaton, who left him in order to become famous. Due to this, poor Blooky has crippling depression.

Missed the memo and is the same difficulty as before.

The tears that go around the walls are almost undodgeable unless you spare him.

25 Mad Mew Mew

This secret boss is actually really tough. The attack patterns are insane, and it makes it worse that you have to use the analog sticks. It's the third hardest fight in the game, in my opinion.

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