Top 10 Best Undertale Bosses

You've stared into their glowing eyes, dodged their bullets, listened to their monologues, and maybe even cried over some of them. Bosses in Undertale aren't just a test of reflexes. They're a full-body, heartstring-tugging, brain-bending experience. Every fight throws something new at you, from sudden difficulty spikes to fourth-wall-breaking insanity. You think you're just battling a character. You're not. You're in a philosophical debate with a murder machine, a quiz show host having an identity crisis, or a time-bending child of god-complex proportions.

This isn't only about who was hardest or who had the best soundtrack. Fine, maybe the soundtrack does carry a little weight. But more than that, it's about the bosses who made you pause. Not just your game. Your entire thought process.

Now it's your turn. Vote for the ones that shook you, challenged you, or made you question your entire moral compass.

The Top Ten

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 serves as a supporting protagonist in the "Pacifist" and "Neutral" routes of the game, and a heroic antagonist and final boss in the "Genocide" route. Sans is known for his... read more

Definitely the hardest boss in the game, probably taking at least 20 or 30 tries to beat the first time, and the one with the best gameplay, with lots of different attacks that require a lot of skill and some pretty good reflexes.
Also, Sans is one of the best characters in the game, and being forced to kill him is kind of heartbreaking, especially with all his dialogue throughout the fight. It's an emotional and stressful ride that we won't be forgetting anytime soon.

A massively powerful monster. I mean, he can throw about 1,000,000 bones, fire deadly Gaster Blasters, use telekinesis (not referring to the Pokémon move), poison you with karmic retribution, teleport, break the 4th wall, and FREEZE TIME! I rank him as the 3rd most powerful Undertale character, but he is still very carefree and lazy, telling bad puns.
I also love his battle song.
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 only television star in the Underground. Mettaton is a popular character within the fanbase, known for his flamboyant personality and dramatic flair. His notable features include... read more

Mettaton is probably the funniest character in the whole game, and his final battle is certainly his climax. Starring his beautiful new body, Mettaton EX is the perfect combination of fun gameplay and funny moments and dialogue. It's also one of the most creative moments in Undertale - the idea of an audience score during the fight is brilliant.

All right! I think we were all expecting Sans, but I definitely think Mettaton is the best. He also has by far the best theme song and, of course, the best legs.
Asriel Dreemurr

Asriel Dreemurr is a character in the 2015 video game Undertale, created by Toby Fox.
He is the biological child of King Asgore Dreemurr and Queen Toriel, but he was believed to have died before the game's events. In the True Pacifist Route, where the player spares every character, Asriel's backstory... read more

Top ten boss fights. Not top ten hardest boss fights. The only way to win is not by sparing him, but by saving him. His track is one of the best in the game - I'm talking about His Theme. A complete masterpiece that deserves better than to be featured in some sad comics and animations that don't have anything to do with Asriel or Flowey.
Also, he has the saddest backstory in the game, with the second being Chara. He is the most powerful boss in the entire game (he has the power of seven humans and can erase existence), and the fight is one of the most epic in the game. Saving someone who seemed irredeemable but definitely wasn't is unforgettable.

This fight is great in almost every way. It's super epic, emotional, and dramatic, making this the perfect climax for the game.
The only thing that bothers me about this battle is it's too easy, which makes it kind of underwhelming at some points. But it's still an amazing experience because of the characters and emotions involved and the AWESOME soundtrack.
Photoshop Flowey

I couldn't possibly have chosen any other boss battle for the top spot. This fight is the perfect final battle for the game: it's hard, it's disturbing (whoever thought of making Omega Flowey a Photoshop abomination is a genius), it's fun, and it's EPIC on a whole new level.
The soundtrack is amazing and fits so well in the fight that it's almost like they made it first and then created a boss battle to match it! Also, making Flowey able to load save files and close your game during the fight makes it even more disturbing and scary. It's just brilliant.
It's not the most emotional fight in the game, nor does it have the best gameplay, but the whole feeling of despair and eventual epicness makes it so satisfying and memorable. The sudden change of graphics also makes it really unique.
Asgore Dreemurr

Asgore Dreemurr is a boss monster and the king of the monsters in the 2015 RPG Undertale, created by Toby Fox. Asgore is portrayed as the main antagonist, with a plan to collect seven human souls to break the barrier trapping the monsters underground. His character is slowly revealed through hints and... read more

This is a boss that is not only difficult, but it's also a pretty emotional one. He's reluctant to fight. He can't even look you in the eye. The music fills the atmosphere, his attacks weaken as your HP lowers, etc. Enough said.

The epic opening, breaking mercy, being forced to fight the kindest monster in the Underground, his final words, the bitter end. No other boss represents Undertale better than Asgore.

I legit got stuck on this battle for like a month because I ran out of food, and it's so hard without consumables...
Papyrus

Papyrus is a character from the 2015 game Undertale, created by Toby Fox. He is the younger brother of Sans the Skeleton, a Royal Guard in training, and a sentry in the town of Snowdin. Unlike his brother, Papyrus is energetic, loud, and somewhat full of himself, but in an endearing and earnest way.... read more

I truly love the Papyrus boss fight. Bonetrousle is one of my favorite pieces of music in Undertale, and it's an extremely funny fight, especially considering that his dialogue is some of the funniest.
What I truly love about Papyrus is that he refuses to kill anyone, which is one of the sweetest things in any game... EVER! Well done, Toby Fox, for creating such an original character.

I really love this boss fight because it's easy and fun! It's pretty amusing, and there are a lot of jokes in there - it gets even better if you decide to flirt with Papyrus! You don't even really need to do anything, as you can just die three times, and precious cinnamon roll Papyrus will spare you anyway. He just can't bear to hurt you, aww.
Undyne the Undying

Undyne is a main character in Toby Fox's 2015 RPG Undertale. She is the fish-like, armor-clad captain of the Royal Guard, devoted to protecting the monsters of the Underground. Her name is a pun on the word "Undying" and a reference to the mythical water spirit, "Undine."... read more

Here's the second hardest boss in the game, and the one who tried to warn us about how frustrating the path we were taking was going to be. The introduction to this fight is really awesome and unexpected because every other character you faced up to this point was instantly killed with one hit. But not Undyne. She just refused to die.

Let's face it. I can't vote for Sans because I haven't fought him yet. And do you know why? Because I can't get past Undyne. I mean, this boss fight is an amazing one to get stuck on, and then you just curl up into a ball of despair because you can't beat it.
Muffet

Muffet is a character from the game Undertale. She appears in the Hotland area, where she runs a bake sale to raise funds for the spider clan. Her goal is to help reunite the spiders from the Ruins with those in Hotland, as they cannot cross the Snowdin region.

Her song is one of the best I've heard in this game, her fight is innovative, and it's fairly challenging. Enough said.

You can even skip this battle. The YouTuber I watched skipped it, and I usually HATE spiders, but today I did some research... Best boss.

Truly amazing song and plot. Couldn't be harder or better for the game.
Toriel

Toriel is a goat-like monster who is a secondary major character in Toby Fox's 2015 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

She's definitely one of the easiest bosses, but also one of those bosses that can really pull on your heartstrings.
Mad Dummy

This thing just looks funny, has great music, and overall is a really fun and hilarious boss fight. I love its attacks.

I have a bone to pick with people who think Sans is the best. Awesome battle theme too.

Probably the most original fight, because you have to use his own attacks against him to beat him.

The Newcomers

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Lesser Dog

Lesser Dog is a character from the indie video game Undertale. He is a member of the Snowdin Canine Unit and becomes increasingly enthusiastic when the player chooses to pet him. As the encounter continues, his neck stretches longer and longer, creating a humorous and memorable experience for players... read more
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Mad Mew Mew

A psychotic training dummy has become... an anime girl? This is a happy twist for Mad Dummy (assuming you spare Mew Mew). If you talk to her later, you'll find that she's becoming more like the character she appears as, and less like, well, Mad Dummy.

The Contenders

Undyne

Undyne is a main character in Toby Fox's 2015 RPG Undertale. She is the fish-like, armor-clad captain of the Royal Guard, devoted to protecting the monsters of the Underground. Her name is a pun on the word "Undying" and a reference to the mythical water spirit, "Undine."... read more
Greater Dog

All of the dogs in the game are so cute!
Snowdrake's Mother
Napstablook

Napstablook is a secondary character from Toby Fox's 2015 RPG Undertale. He is a melancholic ghost and the cousin of Mettaton, who left to pursue fame. Napstablook is characterized by his low self-esteem and depressive personality, often staying at home and enjoying music.
Mettaton NEO

He attacks if there's an audience and if you do nothing in the fight.
Reaper Bird
Memoryhead
Endogeny

Endogeny is a minor character from the indie game Undertale, which was developed by Toby Fox. It is one of the "Amalgamates," a group of monsters that have been fused together as a result of unethical experiments.
This creature appears as a disturbing blend of several dogs and is encountered in... read more
Lemon Bread
So Sorry
Glyde

One of the more "interesting" characters. A secret boss, but thought of as a normal encounter.