If anyone doesn't know how to solve it, on the bottom level, it says, "Don't step on the leaves." On the top level, don't step on the areas that had the leaves. Memorize the path on the downstairs area, and you can make it through the top area.
So basically, if you dick around enough, the game dicks back. I would pay admission to see the game grumps versus undertale. I know they did it on steam train, but man, wouldn't "Arin and danny versus undertale's mechanics" be kinda funny?
If you fuck around with all these tiny things like walking out of the ruins before talking to Toriel, the game just gets real tired of your shit. Same thing happens to the training dummy at the start of the game.
I'VE BEEN AT THIS PUZZLE FOR 10 MINUTES AND I CANT FREAKING SOLVE IT AND MY DAD WHOS PRETTY GOOD AT PUZZLE GAMES DOESNT KNOW EITHER AAAAAAAAAAAAAAAAAAA
Did you do sparing asriel? If not, it's really funny! Just hack a save so you have the real knife, and you can spare asriel once it comes for you to save yo friends, thanks for reading!