"In a world of monsters, who can you trust?"
Five Nights Underground is a game by FazbearFreak. It is a crossover game featuring characters from the game Undertale.


Many years ago, two races ruled over Earth: humans and monsters. However, war broke out between the two races, and the monsters were sealed underground.

However, you have been sent down into the monsters' domain to end them once and for all. The choice is yours: will you try to befriend the monsters at risk of being executed, or will you murder them all to satisfy your leaders?

Either way, this is your tale. You have five nights to meet your goal. Do it, or die trying.



"Your best friend in the underground. Follow his advice, and you'll be rewarded."

Flowey is a small flower with a white face, yellow petals, and a green stem.

Unlike most other monsters, Flowey does not usually act as a threat towards the player. Instead, he will appear in the player's office and serve as the Phone Guy each night. He encourages the player to slaughter the rest of the monsters and promises a reward if they do so.

Flowey only becomes a threat towards the player in the Neutral Ending's version of Night 6, where he becomes Omega Flowey.


"A motherly goat who lives in the Ruins. She knows what's best for you."
Toriel is a white anthropomorphic goat. She wears a purple dress with the Delta Rune on it.

Toriel starts on CAM A8, and becomes active on Night 1. After leaving CAM A8, she will move in this order:

  • CAM B6
  • CAM A1
  • CAM B3 (position 1)
  • CAM B3 (position 2)
  • CAM B3 (position 3)
  • Right Blindspot

When Toriel appears in the office, the player must either spare her or kill her to avoid a game over.

Spare Minigame

Toriel's Spare Minigame requires the player to catch eight slices of pie in ten seconds using the blue SOUL. The slices will fall from the top of the screen, and the player cannot jump.


"A shy ghost who loves listening to music. He also likes racing snails."
Napstablook is a white ghost who wears black headphones.

Napstablook starts on CAM A2, and becomes active on Night 1. After leaving CAM A2, he will move in this order:

  • CAM B2 (position 1)
  • CAM B2 (position 2)
  • CAM A6
  • CAM B2 (position 3)
  • CAM B2 (position 4)
  • Left Blindspot

When Napstablook appears in the office, the player must either spare him or kill him to avoid a game over.

Spare Minigame

Napstablook's Spare Minigame requires the player to engage in a small snail race. The player needs to mash the left and right arrow keys quick enough to beat the opposing snails.


"A lazy skeleton who loves making puns and pulling pranks. There's more to him than it seems..."
Sans is a short, chubby skeleton. He has white pupils, a blue hoodie, black shorts, and pink slippers.

Sans starts on CAM A7, and begins moving on Night 2. After leaving CAM A7, he will move in this order:

  • CAM B4 (position 1)
  • CAM B4 (position 2)
  • CAM A6
  • CAM B2 (position 1)
  • CAM B2 (position 2)
  • Left Blindspot

When Sans appears in the office, the player must either spare him or listen to one of his jokes (the latter takes about seven seconds) to avoid a game over. Trying to kill Sans will result in him dodging the attack and killing the player.

Spare Minigame

Sans' Spare Minigame requires the player to play a Tetris-style minigame where they must stack hot dogs. Once the player places down all 20 hot dogs, they complete the minigame.


"A friendly, yet ambitious skeleton who dreams of being in the Royal Guard. Also likes spaghetti."
Papyrus is a tall skeleton who wears white armor and a red cape.

Papyrus starts on CAM A5, and becomes active on Night 2. After leaving CAM A5, he will move in this order:

  • CAM B3 (position 1)
  • CAM B3 (position 2)
  • CAM A1 (position 1)
  • CAM A2 (position 2)
  • CAM B1
  • Center Blindspot

When Papyrus appears in the office, the player must either spare him or kill him to avoid a game over.

Spare Minigame

Papyrus' Spare Minigame is a game of Pong between the player and Papyrus, with a meatball being the ball and pieces of spaghetti being the paddles. The player beats the minigame once they get three points, and they lose if Papyrus gets three points.


"The leader of the Royal Guard. Swears revenge against humanity for [REDACTED]."
Undyne is a blue anthropomorphic fish. She has a red ponytail, a black tank top, and blue jeans.

Undyne starts on CAM A5, and becomes active on Night 3. After leaving CAM A5, she will move in this order:

  • CAM B3 (position 1)
  • CAM B3 (position 2)
  • CAM A1
  • CAM B2 (position 1)
  • CAM B2 (position 2)

On Night 3, Undyne has different behavior than that of the other monsters. Instead of being able to be spared or killed, Undyne will instantly attack the player when she enters the office. However, the player is able to block her spears by using the left or right arrow keys. Between spear strikes, the player has a very small window of time when they can strike Undyne and kill her.

On Night 4 and 5, Undyne acts like the other monsters and gets her own Spare Minigame.

Spare Minigame

Undyne's Spare Minigame is similar to her battle from Undertale. The player will have to block her spears for a short period of time to complete the minigame. However, the player can only be hit three times before they lose.

Undyne the Undying

Undyne the Undying is a form of Undyne only seen on the Genocide Route. In her Undying form, Undyne wears a suit of armor with a piece of the Delta Rune acting as her shoulderpads.

While in her Undying form, Undyne can summon spears that act as enemies. They can enter from the left or the right, and failing to block them results in an instant death.


"An anime-loving lizard, and the Royal Scientist of the Underground."
Alphys is a yellow anthropomorphic lizard who wears black glasses and a lab coat.

Alphys starts on CAM A2, and becomes active on Night 4. After leaving CAM A4, she will move in this order:

  • CAM B2 (position 1)
  • CAM B2 (position 2)
  • CAM A1
  • CAM B1
  • Center Blindspot

When Alphys appears in the office, the player must either spare her or kill her to avoid a game over.

Spare Minigame

Alphys' Spare Minigame is very similar to the game Space Invaders. The player controls the Yellow SOUL in order to destroy Mettabots, who will fire at the player. Getting hit three times will make the player lose the minigame.


"Dr. Alphys' greatest creation. Enjoys showbiz and drama."
Mettaton is a robot who is shaped like a gray box. He has two hands, a screen serving as his face, and a wheel underneath him.

Mettaton starts on CAM A2, and becomes active on Night 4. The player must continuously check CAM A2 to stop Mettaton from becoming active. If Mettaton becomes active, he will rush into the Office. When he does so, he will block the view of the Flashlight for a short time, as well as slowly fill up the Awareness Bar.

The player can kill Mettaton if he is currently in the Office.


"King of the monsters."
Asgore is a white anthropomorphic goat with a yellow beard. He wears a purple robe and a crown. He also usually wields a red trident.

Asgore starts on CAM A1, and becomes active on Night 5 (from 4 AM onwards). He can enter any room and attack from either of the Office's three entrances. The player cannot spare Asgore, but they can block his attacks and/or try to kill him.

Final Bosses

The game has three final bosses, with one being fought on each route.

Asriel Dreemurr

Asriel Dreemurr is the final boss of the Pacifist Route, and is a goat-like being made out of every soul in the Underground. He wears a black robe with the Delta Rune on it.

Asriel Dreemurr can move to any camera, and will attempt to slash the player with a sword when he gets into the Office. He also has control over "Lost" versions of:

  • Toriel
  • Sans
  • Papyrus
  • Undyne
  • Alphys
  • Asgore

In order to spare Asriel Dreemurr and complete the Pacifist Route, the player must complete a harder version of each Lost Soul's Spare Minigame.

Omega Flowey

Omega Flowey is a giant plant monster with a TV for a head and red thorns along his arms. He also had bloodshot eyes and multiple tubes attached to his "body".

Omega Flowey is the final boss of the Neutral Route, and can move to any camera. His method of attacking is approaching the blindspots and shooting his arms out towards the player. The player must be prepared to block Omega Flowey's attacks or be killed.


Sans is exactly the same as he was before, but he lacks pupils.

Sans can teleport around the building, and shoot Gaster Blasters from any of the office's entrances. He can also teleport into the player's office and trigger a minigame where the player must dodge bones.

Sans cannot be killed or spared until the player reaches 6 AM, where he will be killed via cutscene.



There are sixteen cameras, grouped into two groups: Group A and Group B. The player can view the cameras to check on the monsters. The cameras have unlimited battery.


The player has a knife that they can use to kill the monsters, rendering them inactive for the remainder of the game. However, each monster increases the AI of some of the remaining monsters by a certain amount when they're killed.

Kills and AI Changes

Monster Killed Toriel Change Napstablook Change Sans Change Papyrus Change Undyne Change Alphys Change Mettaton Change Asgore AI Change
Toriel N/A 0 +2 0 0 0 0 +5
Napstablook 0 N/A 0 0 0 -2 +4 0
Sans N/A N/A N/A N/A N/A N/A N/A N/A
Papyrus 0 0 Deactivated until Night 6 on a Genocide Run N/A +4 0 0 0
Undyne 0 0 0 +2 N/A -5 0 +3
Alphys 0 0 0 0 +5 N/A +5 0
Mettaton 0 +3 0 0 +2 Deactivated N/A 0
Asgore +2 0 0 +2 +5 +1 0 N/A


If a monster appears in the office, the player has the option of sparing them. If they choose to do so, they will engage in a small minigame. If the player beats the minigame, the monster leaves the office. If the player loses, the monster leaves, but the player gets a strike. If the player gets three strikes, they get a game over.

Completing each minigame is also a requirement for the Pacifist ending.

Awareness Bar

The player has an awareness bar that'll rise if a monster is in the office. If the awareness bar rises fully, the player gets a game over.


The player has a flashlight they can use to illuminate the three doorways in the office, as well as the cameras. However, the flashlight has a limited battery.

More info soon...


Night 1

Flowey's Message

First Playthrough

"Howdy! I'm Flowey! Flowey the Flower! Golly, it looks like you're new to the Underground! I guess little ol' me will have to teach ya a few things!"
"First of all, there's a flashlight and a knife on your desk. You can use the flashlight to see into the many hallways around you. It can also be used to illuminate the cameras where those pesky monsters will be roaming around. If a monster gets into your 'office', you can use the knife to slaughter them! Sure, you CAN find an alternative to killing them, but where's the fun in that?"
"Tonight will be simple. There's two monsters: a goat and a ghost. Don't worry, they're harmless for the most part. However, your bosses might get suspicious if you let the monsters hang around for too long. We wouldn't want THAT to happen, would we?"
"Alright, I think you got the jist of it. Good luck, buddy!"

Subsequent Playthroughs

"Howdy! I'm Flowey! Flowey the... wait. Why am I telling you who I am? You already KNOW who I am. Golly, it's quite an honor to get to see you again. Say, why DID you reset everything anyway? Did you want to see what would happen if you did things a bit differently? If ya did, I can't blame ya. I wonder what you'll do differently this time..."
"This is gonna be fun for both of us."

Monster AI

Only Toriel and Napstablook are active on this night.

Monster AI Level
Toriel 3
Napstablook 2

Night 2

Flowey's Message

If no one was killed

"So, you decided to spare the monsters? Well, that's fine, at least for now. However, I gotta warn ya: Sometime soon, you'll meet a TRUE threat who probably won't take your mercy. What are you doing to do then, smartypants? Will you kill out of frustration, or will you still try to spare them? The choice is yours, but choose wisely..."
"I'd HATE to see you get killed."

If Toriel was killed

"Hmmmm... you're on the right track, but you only killed that pathetic excuse of a mother. Why did that idiotic ghost deserve your mercy, but not her?"
"Oh, I see. You think that just because you didn't kill EVERYONE means that you're still a good person. Hee hee hee... It's funny that you think that, since it isn't true at all. You're on the path to becoming a monster just like me."
"I mean, you COULD always reset everything, but you'd still remember the look on Toriel's face as you slaughtered her... Well, it's your choice. I hope you make a good one."

If Napstablook was killed

"So close, yet so far. You only killed that foolish ghost. Why couldn't you have killed that goat too?"
"Oh, I see. You think that just because you didn't kill EVERYONE means that you're still a good person. Hee hee hee... It's funny that you think that, since it isn't true at all. You're on the path to becoming a monster just like me."
"You know, if you want him back, you could always just reset. Then again, you would still feel guilty about slaughtering an innocent monster... unless you don't feel anything at all."

If Toriel and Napstablook were killed

"Hee hee hee... I KNEW you'd make the right choices. You see, in this world, it's kill or be killed, and you've learned that very quickly. I'm proud of you, partner."
"Anyway, tonight, those stupid skeletons from Snowdin are coming to visit. The tall one's not that big of an issue, and can be killed rather quickly. But that smiley trashbag... let's just say he's caused me quite the amount of trouble. Just make sure you watch out for him."
"Alright, good luck! I'll be watching..."

Monster AI

Monster AI Level
Toriel 5
Napstablook 3
Sans 2
Papyrus 4

Night 3

Flowey's Message

If no one was killed

"Well, even after my warning, you still haven't learned a thing. You know that in this world, it's kill or be killed, right?"
"Well, listen, buddy. Tonight... SHE'S coming after you. Trust me, she won't be spared as easy as those stupid brothers. In fact, I think she's going to try and kill you herself. If you don't wanna die, make sure you block her spears quickly. Between strikes, you JUST might be able to get a good hit on her. Of course, you wouldn't hurt anyone, would you? PATHETIC."
"Good luck, pal. I hope you learn something from all this."

If 1-2 monsters were killed

"Hee hee hee... you've been doing a good job so far! I wonder why you didn't kill ALL the monsters, but [insert number of kills here] is a start!"
"Listen, you know the head of the Royal Guard? Well, she doesn't particularly like humans too much. In fact, if she catches you, she'll probably try and kill you. Don't worry, though! As long as you have good reflexes, you'll be able to block her attacks and kill her!"
"You ready for this? Well, we'll see..."

If 3 monsters were killed

"Well, looks like you killed almost half the monsters. That's pretty impressive! Y'know, you remind me of someone who fell into the Underground once. They were pretty nice, but were quickly corrupted into killing everyone. THEN they reset the timeline so she could do it all over again. Of course, YOU wouldn't try doing that, right?"
"Oh, what's their name? Well, their name is... *metallic footsteps* Oh golly. Well, buddy, I should have mentioned this earlier, but Undyne's REALLY mad at you. You didn't hear this from me, but after all of that killing you did, she wants to wage war on humanity even more."
"Be on guard tonight. You're going to need to use all your skills to survive against HER."

Monster AI (Pacifist-Neutral)

Monster AI Level
Toriel 8
Napstablook 6
Sans 4
Papyrus 6
Undyne 7

Monster AI (Genocide)

Note that at 6 AM on this version of Night 3, Undyne is instantly killed.

Monster AI Level
Toriel 0
Napstablook 0
Sans 0
Papyrus 0
Undyne the Undying 10

Night 4

Flowey's Message

If no one was killed

"Are you freakin' kidding me right now? Even UNDYNE couldn't kill you? Why can't you just DIE already?"
"Well, if you really want to waste your time with that mercy garbage, I guess nobody here can stop you. You've already befriended most of the monsters, and that 'Royal Scientist' will be easy to spare. Just make sure you keep an eye on that robot of hers..."
"Alright, that's it. Good luck, pal."

If 1-4 monsters were killed

"Alright, you've made it to Night 4. Y'know, you're running out of time to kill all the monsters. You might wanna get a move on before your time is up..."
"Then again, I bet you didn't want to kill ALL the monsters. Maybe you found Papyrus annoying, so you killed him. On the other hand, maybe you killed Undyne just to keep yourself alive. Well, how about this: those people MEANT something to others. If you feel bad about it now, I have a little idea that could help you."
"Just finish the job."

If 5 monsters were killed

"We're almost done here, partner. We've only got three more idiots to kill. Tonight, that Royal Scientist and her little robot will start moving around. The robot might give you a little bit of trouble, but I bet he won't hurt you if you keep watching him. As for the Royal Scientist... you know what to do."
"Good luck."

Monster AI

Monster AI Level
Toriel 10
Napstablook 8
Sans 6
Papyrus 9
Undyne 11
Alphys 4
Mettaton 5

Night 5

Flowey's Message

Regardless of the player's actions, Flowey's message will always be the same on this night.

"Alright, last night on the job. You know, I really gotta thank you. Everything has fallen into place. My plan will finally become reality, and it's all thanks to you."
"See you soon, partner."

Monster AI

Note that at 4 AM (12 AM on a Genocide run), all the monsters are replaced with Asgore. Killing Asgore after 4 AM will either resume all the other monsters (if the player is on a Pacifist/Neutral run) or end the night (if the player is on a Genocide run).

Monster AI Level
Toriel 12
Napstablook 10
Sans 10
Papyrus 11
Undyne 13
Alphys 8
Mettaton 8
Asgore 10

Night 6 (Pacifist)

Flowey's Message

"You IDIOT. Even after I warned you countless times, you still went ahead and spared the monsters. Well, that's fine. I guess I'll have to teach you a little lesson of my OWN!"

Monster AI

Monster AI Level
Asriel Dreemurr 15
Lost Toriel 10
Lost Sans 10
Lost Papyrus 10
Lost Undyne 10
Lost Alphys 10
Lost Asgore 10

Boss Battle

After Flowey becomes Asriel Dreemurr, six "Lost Souls" will begin to wander the map along with him. Asriel cannot be spared until all six Lost Souls are spared, which requires the player to beat a harder version of each soul's Spare Minigame. There is also no time mechanic, meaning that the player must spare all six souls before they can complete the night.


Asriel appears before the player and speaks to them:

"Ha ha ha... I know what you're here for. You want to take her away from me. Well, I won't let you! TAKE THIS!"
The screen starts to fade to white. Then, the screen cuts to a first-person view of a man awaking in his bed. He looks around the room before dismissing the game's events as a dream before going back to bed.

The credits then begin to roll as "Last Goodbye" plays in the background. After the credits roll, a scene of Frisk running up to Mt. Ebott can be seen.

Night 6 (Neutral)

Flowey's Message

"Howdy! Again, I wanna give you a HUGE thanks. While you've been having your fun, I stole the six human souls! That's right, six humans fell down before... SHE did. Anyway, all I need is one soul before I become GOD."
"What's that? You want me to STOP? Hee hee hee... you really ARE an idiot."

Monster AI

Monster AI Level
Omega Flowey 15

Boss Battle

Omega Flowey will try to attack the player throughout the night, and they will need to dodge his attacks. However, in order to progress, they must find the six human souls scattered around the map and free them (a reversed version of the Music Box from FNaF 2). Once the player frees all six souls, the time mechanic will start up as normal, and the player will need to survive until 6 AM to beat the night and defeat Omega Flowey.


After being turned back to normal, Flowey will appear.

"I just don't understand. Even with all that power, I couldn't kill you. But... how? I should have killed you again and again!"
"Wait, I see. You have the same qualities of her soul. That's how you've been evading me this whole time. You must think you're REAL clever, buddy, but the jig's up."
"Now DIE."
Flowey impales the player with vines, killing them. The credits will begin to roll before the player is sent back to the title screen.
Five Nights Underground
By FazbearFreak
based off of Undertale by Toby Fox and FNaF by Scott Cawthon
Thanks for playing.

Night 6 (Genocide)

Sans' Message

Instead of Flowey, Sans will speak to the player before the night begins.

"So, you've been busy, huh? Well, pal, I know why you came down here in the first place. You wanted to see her again. However, that really doesn't excuse you from killing all my friends."
"Y'know, you kinda remind me of her. She killed all the monsters and quickly became addicted to it. You, on the other hand, did this just because you wanted to. Listen, I'm gonna ask you the same question I asked her..."
"Do you wanna have a bad time?"
"Considering everything you've done so far, it looks like ya do. Welp, here we go."

Monster AI

Monster AI Level
Sans 19


Sans will teleport in front of the player, but is quickly slashed by the player. Sans will start crumpling to the floor as he speaks:

"Welp, I guess I shoulda known this would happen. If her determination led her to this point, yours pushed you WAY beyond that. Hey, do me a favor. If you end up resetting the timeline, don't tell anyone about this, okay? Thanks. Anyway, I'm going to Grillby's."
"Papyrus, do you want anything?"
Flowey will appear as Sans turns to dust. Flowey will then begin to speak.
"Good job! It looks like you FINALLY took out that smiley trashbag. Took ya long enough, but better late than never! Y'know how I said I'd reward you for all this? Well, it's your lucky day! I brought HER back, just for you. You can thank me later!"
Flowey disappears into the ground as a red smiling face appears in the center hallway.
"So, after all this time, you came for me, father."
"Thank you for this."
The game then crashes.



Here, the player can view all the monsters they've encountered throughout the game, as well as play their Spare Minigames.


Here, the player can view all the cutscenes that they have unlocked.

Custom Night

On this night, the player can customize the AI of all the monsters. However, the Knife is unavailable on this night, forcing the player to try and spare the monsters. Beating this night on 8/20 mode will result in the player gaining a star on the title screen.


  • This game is one of FazbearFreak's biggest games.
  • The ending of the Genocide Route implies that the player controls Chara's father.
  • This game also had the longest development period of a FazbearFreak game, taking nearly a month to complete.