Yooooooo this game is really cool! The art was really well done, the backgrounds and characters/enemies, UI sfx, it all looks really clean! Funny and charming game.
The mechanics felt really good too, the yoyo is very unique and the groundpound is very satisfying.
While I did like the simple way the controls were written in the environment, it did lead to some confusion; when I got the run button I mistook it for a dash and couldn't figure out how to use it properly. At the very least the signpost needed a "hold" or "run" to be written on it.
I ended up falling down the pit with no way back up, frozen there by the checkpoint, no way to make any jumps, and I almost quit in frustration. The run speed and animation are also pretty subtle, especially compared to the initial burst animation. I do think something extra to the run could give it that oomph to make it undeniably clear, maybe a dust particle that comes continuously out of the feet or a scampering sound effect or something? Just a suggestion.
Once I DID figure out running though, it was very satisfying to flow between platforms. The character that felt oppressively heavy before started to click and it was very fun!
There's one part where you unlock a fork with a key, I didn't really understand why a key removes a fork, I had kinda assumed the fork would be indicative of another move to get through but alas.
Some kind of bug happened during the boss fight my second try, I ground pounded him at the start and then ended up floating backwards into a wall, not able to move and not taking any damage, softlocking me :(
I did beat him though! He was uh.... exceptionally easy. He basically gets stunlocked simply because you can hit him no risk as soon as he gets out of stun. My recommendation would be to not have a stun state at all, but instead to disable his hurtbox for a bit when he's hit (but still flashes or something to indicate he's taken the hit) and have him continue attacking. That or switching back and forth between vulnerable and invulnerable states that can't be interrupted. The art of him getting hit was pretty funny though.
I think as a metroidvania it was a little barebones, largely because you give the player running and yoyo right at the start. The only item/obstacle combo really was the ground pound; when I booted up the game after crashing at the boss and losing all my progress I managed to get right back where I was in about a minute, since all I really had to do was run straight to the one key and the one ground pound. If you take the path of least resistance (the tower of cats is easier to fight than jumping up the platforms before knowing the run button), you also never even encounter the breakable blocks until you already have the powerup, so there's no real feeling of an area being gated or any moment of 'ah, I remember where I can try this'
I'd love to see more mechanics, I think you've definitely got some good ideas and I'd love to see more!