Neat little game! It's like a cute combination between a Metroid game and something like Minit's speedrunning time loop structure. Overall I felt like this was a nice short and sweet experience, where I kept delving down different routes, collecting power-ups, opening up shortcuts, and eventually finding the diamond, whereupon I had to plot out a route to get in and out quick enough like some sort of heist, haha!
While it was all good, I did find the design a bit confusing. It just felt a bit odd that, due to the way the world is constructed, you only find the diamond when you've pretty much collected all of the upgrades necessary to get it out: before then, you don't even know what the goal is and why you're collecting all this stuff in the first place, so it's somewhat aimless. And why does the time loop structure happen before you've even collected the diamond? You'd think it only needs to happen then, like some sort of alarm. Basically, I almost feel like the diamond should be introduced in some manner earlier to setup the premise: like maybe you have easy access to the diamond, but getting it out is impossible without upgrades, so you make the decision to leave it for now and instead go into another part of the cave and get upgrades and set stuff up first. Eh, it worked out in the end, I suppose, but still, food for thought!
Oh yeah, as a side note, the jump physics felt really wonky and difficult to control: eventually got used to them, but yeah, wish they were a bit more intuitive.