This is by no means a comprehensive list! These are just the things I have found while perusing the data found within the switch edition of the game. Major changes are bolded for emphasis. The following contains spoilers (obviously) so don’t keep reading if you want to find the new things yourself!

The addition of the Mad Mew Mew fight (dialogue, scripts, objects, etc.)

Mad Mew Mew also has a spot in the end credits, adding one more possible yellow name.



Also, this unused bit of dialog which needs to be shown to the world:



So Sorry now has dialogue post-pacifist.

He also will appear at any time of day rather than just at 8PM now. (I’m actually really happy he finally gets some more attention!)

Clamgirl has a new sprite, labeled “clam_goner_b”, as well as a new FUN event.

This event will occur if you meet all the other requirements for seeing Clamgirl (A Lv. of less than 8 and a fun value between 80 and 89), have talked to her previous to beating the game and then come back, and specifically have a fun value of 81.



In this event, she mentions [in reference to Suzy, her neighbor’s daugter] “But don’t despair, for the time you will meet her…” (her sprite turns gray) “…is fast approaching.”

There are a couple of new borders, including one themed around Mew Mew Kissy Cutie as well as one themed around Tobydog/Annoying Dog

The game has been updated from Game Maker Studio 1.4 to Game Maker Studio 2.

This was necessary for the Switch version to happen. As a result, many many many things have been shifted/restructured. This should also improve some performance, add some additional functionality possibilities, etc. This was also a good move since GMS1.4 is no longer supported.

The credits have been changed a bit in general, shifting around some names, changing the contributions, and adding some staff to localization.

On that note, the Japanese strings have changed in several spots. It appears to be some touchups on the localization.

MANY duplicate sounds/sprites have been removed.

As a sidenote, I think this adds some validity to the unused content still left in the game - a lot of it is very odd (and in two cases, uses Wingdings), and I’m thinking it’s only “unused” in the sense that you can’t see it without datamining. Tl;dr, most unused content left in the files still serves a story purpose.

Looots of objects have added events. These basically all consist of a script call “event_inherited()”. This is a script to ensure that objects with a parent will override certain variables and still function properly. In other words, not something to really pay attention to.

My thoughts - it looks like the changes, besides Clamgirl and MewMew, were pretty much all optimization, cleanup, and transfer to GMS2. This would have taken quite a bit of effort and if I had to venture a guess, was probably one of the bigger reasons Undertale stuff has had such a long silence (not even just the game itself - things like the kickstarter goals as well)

I think we’re coming up on something major that’s been approaching for quite a while ( fast approaching, even ;) ) and I can’t wait for it.

To finish things off, allow me to share one of the best variable names I have ever seen: