Nick's Sonic Fanon Wikia

After playing through Undertale about 9 times, I finally made my list of the top 10 toughest bosses to beat.

In the words of everyone's favorite skeleton, "Here we go".

Number 10[]


Toriel is like the second boss of the game.

She can rough you up, but you should be able to beat her.

Number 9[]

Undyne The Undying

Or genocide Undyne. This variant is quite a bit easier than the pacifist or neutral fights with her.

Mostly because you have more HP to survive her attacks.

Number 8[]

Mad Dummy

Simply put, the Mad Dummy will FUCK YOU UP if you're not prepared for the fight with it.

However, if you're prepared, you'll dispatch this dummy with ease.

Number 7[]


This is the pacifist/neutral route fight with Undyne. She hits the same as in the genocide route. But you have less HP and will have to keep fighting her until you can escape from her.

Number 6[]

Mettaton EX

Face it, Mettaton EX is the hardest version of Mettaton. This fight can easily drag on and kill you by depleting all of your items that restore HP.

Plus Mettaton EX's attacks are quite over the top and you can easily find yourself at a game over screen before you even get to EX.

Number 5[]


Muffet is one of the hardest fights to win on ANY of the routes. However, Muffet comes in at 5 because of an exploit.

If you bought that spider donut way back in the ruins, then all you have to do is survive for about 3 to 6 turns and you win.

Trying to actually fight Muffet is tough, but can be done if you know the game well enough.

Number 4[]


You're probably re-reading this right now to see if you accidently skipped down a number or 2.

You didn't.

Asriel may be the true final boss of Undertale, but he has the distinction of being the ONLY fight in Undertale that CANNOT lose.

Every time you die, the heart will just re-attatch and say "But it refused".

Since you can't lose this fight, Asriel is only this far because of the difficulty to DODGE his attacks.

Again, Asriel can fuck you up in 2 to 3 hits due to your low HP.

Number 3[]


Asgore IS a tougher fight than both his ex-wife and his son.

Toriel holds back and Asriel can't really kill you.

Asgore doesn't hold back and CAN kill you. His rapid-fire attacks and vicious spear swipes will mess you up if you weren't prepared for them.

Plus Asgore is the first boss you fight that breaks the 4th wall by destroying the mercy button.

Number 2[]


Sans makes Asgore and Muffet look easy. When you play genocide, 75% of the players did so just to fight Sans.

Sans is basically the judge of your character's life. On all 3 routes, he judges you before the fight with Asgore. Depending on how many monsters you killed, depends on how it goes.

If you spared more monsters than you killed, Sans will let you past. If you killed more than you spared, prepare to have a bad time.

Sans gives the player fear with his popular "On days like these" speech before declaring that your evil soul should be burning in Hell.

Then after a roughly 15 minute fight, Sans will use his litteral nothing attack. After he falls asleep from boredom, you move the box down to the fight option and attack, which misses, but the accidental second slash defeats Sans.

Before Sans walks off screen, he admits that he knew that he couldn't beat you and then walks away.


Honorable Mentions[]



Greator Dog

So Sorry

Number 1[]

Omega Flowey

If you want the most challenging final boss of them all, play on the neutral route. After beating Asgore, Flowey will appear and finish Asgore before using all 6 souls to transform into this abomination.

Omega Flowey is the longest fight of the game and it is so hard to survive the whole way through. The only good thing is that you get 3 lives in order to first weaken Flowey by turning each soul against him 1 by 1. then with his defence lowered, you have to keep striking while avoiding attacks that cover the entire screen.

Good luck with beating Omega Flowey on your first try without dying once.



"You did this".

"And it cannot be undone".

"For now I am nothing".

"I only want to have some fun".

"Just... like... you".

Oh yes, I couldn't just end it here.


The fight is as long as Omega Flowey, as brutal as Sans, as over the top as Asriel, and as chaotic as Asgore.

Gaster is the final test left behind only for the best to face. If you manage to beat Gaster, then you are probably the true fallen child.

It took me like 5 tries to finally beat Gaster. Every other boss I beat on either my first or second try. Plus Gaster literally throws EVERY GAME MECHANIC AT YOU!

You'll have to shoot, dodge lasers, block arrows, stay still during blue objects, move during orange objects, and survive like 20 chaotic rounds of his attacks in order to win.

Like I said, Gaster is Undertale's final challenge for those that desire a tough battle that they can't win easily.

Well that does it for this top 10, I mean 11 list of the hardest fights in Undertale.

(Dio) Welp, I'm going to Grillby's.

Jules, do you want anything?