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 boss fight, bad puns, and the phrases "geeetttt dunked on!!!" and "you're gonna have a bad time." He is also named after the font "comic sans." Known for also being Ness from the Mother series. (known as Earthbound in Western territories.)

Makes the game a nightmare. I already got stressed on Jevil's fight in Deltarune Chapter 1, but God Sans is hard. Just seeing the beginning wants to tell yourself you're going to die. Oh, one last thing - the song hits hard like how in Deltarune the boss's song like "The World Revolving" (Jevil) or "Big Shot" (Spamton Neo). So yeah, Sans is truly the hardest Toby Fox boss in both games, harder than that one YouTube video that keeps spamming on my Home Screen where it's 3 Jevils at once.

I couldn't get past the final gaster blaster circle for SO long. Weeks after my first attempt on 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. And 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.

What the list should actually be.
1. Sans - Extremely Hard (30 Tries)
2. Undyne the Undying - Almost Always Need Items (20 Tries)
3. Muffet - Was Struggling Lots (14 Tries)
4. Mad Dummy - Very Hard, Only Had Astronaut Food Though (12 Tries)
5. Asgore - Needed Tem Armor (9 Tries and Google Help)
6. Mettaton Ex - Easy After Learning To Always Boast (8 Tries)
7. Omega Flowey - Honestly, Pretty Easy (3 Tries)
8. Undyne - Easy Once You Know What To Do (2 Tries)
9. Toriel - Spared Her Straight Away (1 Try)
10. Papyrus - Don't Think You Can Die (1 Try)

Real top ten list.
1. Sans (50-200 attempts on average)
2. Undyne the Undying (10-40 attempts on average)
3. Asgore (took me 1 attempt somehow, I used all my healing though)
4. Photoshop Flowey (took me 1 attempt, did this boss like an hour ago)
5. Mettaton (took 4 attempts, but didn't feel as difficult as the ones above)
6. Muffet (1 att, I will admit, I had ran out of food, and didn't know you could skip the fight with a spider pastry)
7. Undyne (1 attempt)
8. Asriel (can't die)
9. Toriel (1 attempt)
10. Papyrus (1 attempt so ez)

2 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 attracting deadly flies swinging cactus hands and shooting barrages of seeds all at once. Well good luck on that one because its pretty damn hard

I had no idea what I was doing with Photoshop Flowey, yet somehow I survived.
Until Finale. I was doing just fine. Then when the fight got easier, I died. I'm so good at this.

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 Toriel and Queen Asgore Dreemurr, but he seemingly passed away prior to the games events. His back story is only focused on in the True Pacifist Route, which means the player does not kill a single character. As a young child, he was a close friend of Chara, a human child that fell down into the Underground and was adopted by the Dreemurrs. As Chara died, Asriel carried their lifeless body up to the human world, but was killed, for the humans thought that it was Asriel who killed Chara. 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 its easy, dodging the attacks is a huge challenge

While you cannot die on 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.

I personally haven't fought Asriel yet because I'm stuck on the sans fight but from what I've heard he is a hard fight until a certain point where you just can't die.

You can die but in asriel's first attack if you die you go 2 attacks back so for asriel's first form you have to live. In his true form, however, id you die it doesn't matter.

4 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 at throughout the players journey and his fate at the end of the game is determined by the choices the player has made.

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 perfect hit.

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

Good god. On my first playthrough, I got through Undyne in 2 tries, The Dummy in 1, and Muffet in 4. Asgore took me 27. Asgore is HARD.

5 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, King Asgore, her best friend, Papyrus, and her love interest, Alphys.

Dang those spears are fast! And you need A LOT of healing for this fight. Undyne really gets a lot of buff! I personally find it the biggest challenge of genocide (yes, above sans)

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.

Dang, man. I'm currently stuck at this unbeatable fish! She's like, second hardest! Asriel's battle is nothing! We can't even die in it. And omega flowey, those act and green healing things are just helping us to not die! The regular undyne is easy! And also mettaton! Well, asgore is... the third? Yeah whatevvah, undyne the undying is second hardest! Ngahhh!

Out of all the bosses I've fought so far, Undyne The Undying takes my vote. Bear in mind that since I haven't been able to get past her yet, I haven't fought Sans or any bosses that only appear in Genocide past Undyne The Undying, but she is easily the hardest so far.

6 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!"

I think I struggled with this boss fight the most. The bullet shooting is very unique and kida hard in my opinion. Probably the hardest boos 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

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 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.

This boss was relatively hard, and totally more difficult than asgore. It is a nice transition into the endgame, as it is not too bad but not too easy.

Hard once you first try but after that, if you got healing items, just pose and you beat mettaton. (by the way bombs are easy)

7 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, King Asgore, her best friend, Papyrus, and her love interest, Alphys.

Waterfall is peaceful without Undyne and Mad Dummy. It should be noted there's a way to skip a part of the battle if you get low hp, or even better if you use a skip with 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 in the right spot.

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

The only way to spare her is running away until your red and then run to the hotland bridge, let her faint, then give her water.

8 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.

Why isn't this higher on the list? To me Muffet is harder than Undyne the Undying. Only if you don't have a spider donut though, I'm talking about her fight not being able to skip it

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 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.

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

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 more.

The only time that I had trouble with papyrus was when I was attempting to do the pacifist route.

No...Papyrus is easy...Plus you can skip his battle and befriend him if you die three times instead..

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

I don't think you can actually die against him - it's impossible.

10 Toriel

Toriel is possibly the easiest fight in the game weather your 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!

Walk in the park, Jut spare her two times or three and done, just super easy attacks and dialog.

Strangely I defeated Photoshop Flowey in three tries but on Tori 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.

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...

I don't need friends! I've got knives!

I'm out of knives.

12 Disbelief Papyrus

This is just a fan made battle.

He is just awesome that's why.

Bones orange bones blue bones orange Gaster blasts sans and Undyne the undying

13 Annoying Dog

Toby fox can hack into the files and make the game impossible if he'd like.

This is actually mist likely the strongest character in the game, he created this world (undertake), 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?

Picked for da memes

14 Froggit

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

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 trys and this froggit, is a hacker, or am I gliched?

Please tell me you are joking.


Mystery Man is Mystery Man. But, if the fandom is right and he is Sans' dad, then he is potentially even harder to beat the Sans.

I mean... I like his lore.

He made the op sans

16 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 player's name, which is Frisk. In the genocidal route (achieved by killing as many monsters as you can without sparing), they appear by the end to destroy the world, which happens regardless of the player's choice or intervention. Due to this, most people see them as a villain.

Okay, I know you never fight chara in undertale, but you saw her in genocide. She one-hit you in the end before you even got to 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 quick.

Legitimately can't get rid of her in your files (unless you do some complex "hacking" stuff) so yeah

17 Ultra Sans

The strongest sans

He is awesome and he is so hard if you think sans is hard try this dude

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 houses the only shop vender for the player to sell items; the strongest armor in the game is also sold here.
19 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 smh

You control Frisk, so you can't kill her. Maybe in fan-games, but not Undertale.

I just didn't know why I beat the game without dying once,even if I run Frisk's soul into the attacks.
She is the best character.

Frisk is easy to beat. Just get her soul to run into something harmful.

20 Dusttale Sans

He has fReAkInG more Determination than you in the fan-game.

21 Flower 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 use on themselves easily! 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!

22 Alphys NEO

She's not even in Undertale!

23 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 3rd hardest fight in the game in my opinion.

I wouldn't know. I played on a computer.

24 So Sorry

I feel so sorry for so sorry. He doesn't mean to fight you. He just ran into you and started the fight

Harder then muffet, undyne, papyrus and maybe asgore but not mettaton

I don't know who he is

This is a secret boss, but it's hard, I can say it's the sixth hardest boss after ASGORE

25 Greater Dog

This is easy all of the attacks just barking when you just used ACT (in pacifist run) I don't know what happens if we do a GENOCIDE RUN. maybe you should try it!.

Honestly I was stuck on this for so ages my 1st run. I was trying pacifist but gave up and went neutral.

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