I’m sorry the game wasn't intuitive enough.
Did you try placing the next slime inside the blast radius (yellow circle)?
Or did you try arranging the slimes in descending order?
And like you mentioned, the player character's name is 'y'
Tried both ways a few times, in case I was understanding the instructions wrong! I gave it another try a little while later (because I felt like I had to be able to do it lol) and was able to do it once, but I think it's just that the placement required more precision than I was expecting. More than just overlapping the yellow circles haha. Not sure which collision box I was missing? but clearly one of them. Anyway, I hope that's helpful if you keep working on it. This is a really cool project! :)