* In the webcomic Sleepless Domain, the protagonist's name is Undine (not named after Undyne), however the Alt Text from Chapter 4 Page 2 jokes about both sharing a similar name

* In Them's Fightin' Herds, Shanty has two alts referencing Toriel and Ralsei

* The Yoki Doll in Seam's Shop was updated to match her redesign in Dweller's Empty Path. Below is the current version.

* The design for the Real Knife you have probably seen around comes from a Steam Badge depicting it as a red glowing knife.

* Frisk's sprite looking the way it does was deliberate

* Toby Fox asked a bunch of different artists to make original artwork for UNDERTALE's Steam cards.

* In the files of Deltarune, you can find barricades that were originally planned for the first Berdly fight, funnily enough one of these barricades contains the same creepy smile you can find in Queen's Basement

Submitted by: JcJack777

* The Annoying Dog makes countless cameos during all of Undertale, here are some of the easier ones to miss.

* In the files of Deltarune you can find a mockup sprite of Berdly during the first Berdly fight. He is using an earlier version of his Dark World appearance where he uses his original feather colors and slighty different eyes. Next to them is a comparison of the two

* Chara's coloring is inconsistent in all of their 'phases'.

* There is a bunch of tileset errors in Snowdin, these are some examples I could find and/or I was told about.

* Upon meeting Chara a second time, they'll be confused as to why you keep recreating and destroying the world, even suggesting a different route. Choosing to NOT destroy it won't change the outcome.

* One if not the first appearance of Chara's name was during the Greenlight Trailer

* There's two instances where Fangamer associates the word 'Cungadero' with cars. Merch isn't canon so this doesn't confirm that is its meaning, just a neat fact.

* The Hat Ralsei Plushie was modified.

* Flowey remembers how he used to efficiently fill a glass of water from when he was alive. Even taking care of Toriel whenever she passed out during a party.

* Going to real.deltarune.com sends you to Starmen.Net.....for some reason.

* You can find a crumpled message in Alphys' Lab, it states 'I KNOW WHAT YOU DID'. It's unknown who wrote this. The most likely candidate could be Flowey towards Alphys.

* There are two instances in Undertale/Deltarune where the triangles of the Delta Rune are inverted. Every other appearance remains consistent.

Submitted by JcJack777

* During a Roblox Developer Conference in 2018, Adam Miller used a bunch of Sans Heads as a visual example of Mesh instancing.

Submitted by: Ivy
Source: youtube.com/watch?v=rUPx01…