In Chapter 3, during the "What's Kris's favorite food?" And "What was Asriel's favorite character in Smashing Fighters?" Quiz questions, when you are hovering over an incorrect answer, Kris will cough and attempt to switch it to the correct one.

There is an unused variant of the song "Digital Roots" which is sped up and has the wind ambience removed. The filename, "spamton_house" indicates it was meant to be used in the room outside Spamton's shop, which in the files is named "room_dw_city_spamton_house"

In the Dark Sanctuary this room has a chest hidden in the darkness that you can interact with. Although it doesn't give you anything.

In the Switch 2 version of the Mike Room, if you aren't already using the JoyCons a switch will appear on the wall letting you change controllers.

The T rank room is different depending on if you visit it after Board 1 or Board 2.

The game "Contract Rush DX", a game by Figburn, a developer for the fangame Undertale Yellow. Features a cameo from the Undertale Yellow character Mo.

In Chapter 4, the dialogue option "I'll never play again" changes depending if you are on the weird route or not.

When Tenna switches through channels rapidly at the end of his fight, on release there was a bug for PC caused by using certain GPUs that would display texture data on the screen instead of the intended static. This has since been fixed.

There is unique dialogue from Ralsei if you check the Titan while its shield is down, and unique narration if you do it again.

On December 24th, 2012, Toby posted the song "tomorrow's holiday" to his tumblr, this same song would later be used in Omori as the song "Merry CD"

Inside the Fangamer Tenna plush is a pipis.

On July 3, 2015 Toby uploaded a file called 67.wav to his website.

In the intro of Chapter 3, if you move right until the couch is off-screen, it will start walking.

In a leaked episode of "My Little Pony: Tell Your Tale" titled "Digital Detox", you can hear the Undertale song "Home" in the background during one of the scenes.