Wow, this game was phenomenal. The detail in the art, music, and animations are all incredible, and the gameplay loop of getting from one side of the screen to the other is satisfying. Once I saw the ending, I figured there was a pacifist ending, which I really tried for. Preventing slimes from falling off the edge, however, proved to be quite difficult. The later levels were also incredibly difficult to do without killing slimes. I wish I could have seen what the ending was like for not killing any slimes, but it was too difficult for me. Not that that's a bad thing!
One criticism I can think of (and I'm really scrounging for something to say here) is that the platforming controls feel a bit bad. Specifically, if there was maybe a quarter of a second of time after leaving a ledge in which the player is still able to jump, I think the game would have felt a LOT better to play.
The only other thing I can think of is that I didn't really understand the purpose of the coins. I felt inclined to avoid them because the pink slime told me to collect them, but some of the coins were placed in places that forced you to pick them up. As such, I went the rest of the game disregarding them entirely, neither avoiding them nor seeking them out, and they didn't appear to change the ending. Were they intended to incentivize players to kill slimes in order to collect them?
Overall, phenomenal game. This is easily one of my favorite entries I've played thus far!!!