Spamton shakes the dumpster before exiting his room in Snowgrave sometimes

Kris has a red eye sprite on their decent into the dark world

if you speed up the choice by 666%, you get undertale. similarly, speeding up mus_toomuch.ogg (i think) by 1200% gives you flowey's theme. flowey's theme is also based on f-u-n from spongebob

In Kris’s light world sprite their right leg is thicker then their left

On the playstation version of Undertale, if you unlocked the secret dog's room under the skelebros's sink and you return there after beating Asriel and if you use the boom box, you will speed up the ost "Reunited".

After the Pacifist route, at the bridge of Waterfall there will be a NPCs who hates modern puzzels and has a puzzle you can't solve if I recall correctly

By hacking the game, it’s actually possible to kill snowdrake’s mom, due to her health being coded differently than the other Amalgamates

Difficulty:Impossible how does the soul turn yellow in the spamton neo fight?

in the demo for Ch1, if you pull out to the save menu before beating the game, and attempt to delete your save but stop yourself when reaching this box in the 1st image, the game tracks this action as THREAT in the code. and if you do it 10 times, G[REDACTED] comments on this

In the CORE there is a room with a laser gate that needs to be disabled to move on, normally there are 2 paths you could take to open it but you can just wait in the room for enough time the gate will disappear.