Well I got 82% with no secrets found, though I had a few ideas where some might be. I just didn't know if this would be the kind of game for them and focused on finishing. Also that spider sprite was nightmarish. I loved the aesthetic, I'm a real sucker for gameboy graphics and this looked awesome.
Now some criticism. There were a few jumps that were a little unfair given the camera was too far up to be able to see the spikes below. So you take a leap of faith and end up on a spike, generally you want that stuff to be fair so you don't get cheap deaths. There was a later one with a bat out of view that I hopped on rushing through, but we can attribute that to my lack of patience.
I also died a few times before getting my second heart to the frogs sitting so close to the doorways. You walk out and walk straight into a frog before you realize they're there. That's not a super cheap death, but maybe if they were even one tile further away it would give people more reaction time.
Last criticism is that the unity round hitbox is fairly noticeable in this game. Is this one of your first attempts at making a platformer in unity to teach yourself? If so, you made it much farther than I did and actually made something to be proud of. Though from what I did learn square hitboxes work better for this sort of game so that jumping is smoother, and you don't get hitched on walls so awkwardly.
That's all, I hope none of my criticisms came off as mean or anything, I really did like it, I just want to give an honest opinion that might help make your game better.