In the Deltarune Chapters 3&4 Piano Scorebook sold by fangamer, the 66th page is left completely blank with text that reads "This page is left blank so you don't have to turn pages in the middle of a song."

In the Japanese version of Deltarune, the title Kris obtains after getting the egg in Chapter 3 has the level positioned on the left of the title instead of the right, which is something no other title does.

During the fight with the Old Man Statue, Susie has different dialogue depending on if you make Kris attack or command her to attack, and when you command her to attack she refuses and the option becomes greyed out.

There is an unused game over cutscene for the shootout segments of TV World, similar to the cutscenes that play when you lose in a minigame on TV Time.

Toby Fox used to have a Facebook page which has now been deleted, this is also where the infamous picture of him in sunglasses and a backwards cap comes from.

In 2015, Roblox made a Facebook post shouting out a recreation of Undertale and a Sans avatar in the game.

There is an unused sprite from Chapter 3 called "spr_kris_door_laugh" using Kris' light world sprite. From the name and the very few times we see the light world in Chapter 3, it seems to be meant to be Kris laughing with their hand against the shelter door.

There is also an essay on Wikipedia about the Toby Fox foam picture incident, it's used as an example of photos of people not allowed to be used on Wikipedia since it can't be used to identify Toby Fox since you can't clearly see how he looks.

The Wikipedia article on Toby Fox just got the "good article" label. Only 0.61% of articles have this label.

In the dialogue script for the Faded Rudinn in Castle Town in Chapter 4, its speaker is "no_name" for most of its dialogue, which is normal for NPC dialogues. However on the dialogue about their color being faded, the game uses the speaker "your" which isn't used anywhere else in the game.

In 2015, someone asked Toby what he thought about people secret-hunting in Undertale, including "hidden boss fights against wingdings," to which he responded "regarding this the very nature of it is shrouded in darkness." which is the same phrase used to tease Deltarune.

Toby once had a livestream dot com account that is now lost media, one of his streams was making a song live about Sephiroth shitting on Kyoto, but the link to the stream never got archived.

As revealed in his 2023 interview with Kikiyama in Weekly Famitsu, Toby Fox's preferred Denny's order is the Grape Parfait, a seasonal item only available in Japanese Denny's restaurants.

There is unused text for when you use the Glass, the Light World counterpart of the Shadow Crystal, in Chapter 3. Which you normally can't do as you never have access to the menu in the Light World in this chapter.

Several years ago a company that makes sticker sets you can get in gumball machines put out a "Krypto Villains" sticker set with unlicensed art of slasher villains, which includes Chara for some reason.

The main visual inspirations for Alphys according to Toby were John Egbert from Homestuck, Lisa Simpson, and "that lizard guy from Super Paper Mario" (Francis) although he admits he has never played Super Paper Mario

There is a 10% chance for Ribbick to say the quotes "A lost and lost and lost girl." and also "A crying and crying and crying boy." after you have used Croak/CroakOnX at least twice. Additionally, the "Lost girl" dialogue does not get translated in Japanese, but the boy does.

The Undertale 10th Anniversary stream soundtrack is now available on Toby's bandcamp, originally it was only available on the 10th Anniversary website.

As revealed in the winter 2025 newsletter, chapter 3 originally didn't have the S-Rank room.

During the Chara jumpscare on the genocide route, the right eye and mouth are incorrectly colored.

In Grillby's, the seat Frisk sits in along with the floor is offset by one pixel.

Toby described the fundamentals of his humor as coming down to "two wacky guys." This goes back as far back as five years old, where he would play pretend by making his left and right hand into different characters who acted as comedic foils to each other.

There is a small chance for the Annoying Dog to show up on the pages Bibliox uses to attack.

The ICE KEY obtained in MANTLE might be a reference to an item of the same name in Banjo-Kazooie. In Banjo-Kazooie the key is hidden and serves no purpose, but if you play Banjo-Tooie after getting the Ice Key, it will transfer to that game and unlocks additional content.

Shuttah's recruit description "Don't scream...! It's not the real monster ..." appears to reference the old Nickelodeon cartoon "Aaahh!!! Real Monsters". Shuttah also holds its eyes in its hands like the character Krumm from the show.

In the True Lab, interacting with things in the fridge room before turning the fan on gives unique dialogue.

The code that opens the Mike door (6453) are the numbers that spell out MIKE on a phones keypad.

In the metadata for most of the songs featured on the Undertale 10th Anniversary Stream soundtrack, the software in the metadata is listed as FL Studio 21, meaning Toby has finally made the switch from FL Studio 10.

In Chapter 3's quiz segments, there is a variable deciding Susie's behavior at any one moment. There are four behaviors, referred to in the code as: "Idle", "follow Kris/Ralsei", "bored/guessing", and an unused behavior "stop copying me!". This behavior doesn't exist for Ralsei.

The track "Hall of Fame" in Deltarune references the Tera Raid theme from Pokémon Scarlet and Violet, which was also composed by Toby fox.

The starting melody of ASGORE was inspired by the song "The Fog" from Persona 4, so much so that one of Toby's project files that only contained the initial melody is called "persona4.FLP"

Susie has unique dialogue if you pray for Rudy without having taken her to meet him.

Toby fox has visited the gaming café 84 Hashi, a secret members-only café frequented by many famous game developers, and allows public tours. A personally signed copy of Undertale is on display there, and Toby also donated to the "84Level-up Fund." to preserve 84 Hashi.

The entrance to the Egg Temple in Mancountry appears nearly identical to the entrance to the Temple of Mana in Final Fantasy Adventure.

All the songs from the sword route as well as Hammer Of Justice are hidden in the Bandcamp listing of the Deltarune Chapters 3+4 OST unless you buy it. This also happened with all the genocide route songs in the Bandcamp release of the Undertale OST.

During the optional extra attacks in his fight in Chapter 4, Gerson word for word quotes his Undertale shop dialogue for when you talk to him about "Hero" on the genocide route.

In the Winter Newsletter Toby said that Tennas original name was "Mr. TV Guy." And this name is referenced in game as one of his quiz options.

Toby once planned for you to be able to "marry" Mettaton, similarly to how you can "date" Papyrus, which Toby recalls previously mentioning during the Kickstarter. Mettaton would have accepted the proposal, but only as a fake photo op to promote himself.

Toby got the inspiration for Tenna talking in "Word Art" from the character P.T. Bridgeport from the comic "Pogo"

When you enter the room with the shelter at the start of Chapter 4, Susie's sprite changes to the one where she isn't smiling, and if you leave she goes back to smiling.

The Rabbick in the Green room that says "Dustin' makes me feel good!" is a reference to the Ghostbusters theme, and potentially also to the Neil Cicierega remix "Bustin'" which repeats this phrase several times.

The sprite for when Ralsei covers his mouth in the Lightners Live "It's TV Time!" track is named spr_ralsei_sing_cuss.

In any track for Lightners Live, if you get the exact score required for any given rank, you'll get a placeholder ? Rank. This is because the minigame is only programmed to give you a rank based on if it's less or greater than a score requirement for a rank, but not if its equal.

Jackenstein's dialogue contains several references. The line "YOU SUDN'T COME HERE" is misspelled almost exactly the same as a line in the video adaptation of the fanfiction "Half life: Full life Consequences." Jackenstein also references Zelda CDI in some dialogue as well.

In a DLC for the game "Get in the Car, Loser!", the Halloween Pencil appears as a guest item provided by Toby Fox. And when upgraded it gives snippets of "a story from another world," which seems to describe the start of Susie and Kris's friendship.

Merry Krismas everyone!

The Chitei De Chill page has updated to have previews of all 20 songs (Link below)

Only in Chapter 1, if any of your party members are at 2 HP, overworld hazards will be unable to kill you.

Toby had planned to make the color of the grid in the background of battles change depending on the area, as opposed to always being green as it is in the final game. This was planned for Deltarune as well, but he forgot to include it.

During the battle against K. Round on the Great Board, if you wait long enough when it initiates its self care attack for the first time, you get your turn back before it heals itself. Which leads to it healing on the next turn and breaking the dialogue box.