Only found one ending so far. Pretty decent for a first level, no wallswims and the shifts all seem to work OK. Good imagination with all those corridors underneath bodies of water or lava, keys on top of piles of gold, fly-infested trees, all very nice. It was a bit odd playing this with no story whatsoever - what are those levers? What am I supposed to be doing? Why am I going places and doing things?..
There were some SGEs, most obviously in x999y1000 (and its counterpart(s)) - look behind the locks. There were also some design problems that made the experience a bit awkward. One was
falling into that pit underneath the lake, the one that is locked with the button you have to stand on for some time. The pit doesn't kill you, so you don't quite know if you were meant to fall there with the eye powerup. And when you come back with that powerup, there's still nothing there! You don't even have to press that button, because the passage to the lever is open anyway. Is that a bug?
Another frustrating place was
the invisible maze above the cave entrance. Mad props for making transparent tiles there, but I was stuck there until I looked at the place in the editor - who would've thought there's a shift! Even if I had suspected it, I would still have to spend a ridiculous amount of time pressing "down" on every tile, searching for the right place.
My final criticism is that the level could've used more details and/or consistency in the visuals. The first screen you posted and the ones near it are very bland, there's just one color in the background. One screen has a couple of clouds, another has no clouds but two birds, and another has nothing... would've worked much better if you aimed for consistency in area design, and all the screens would've had clouds (and preferably more realistic than the ones you have there) and a bird or two. And then you go under the lake, and wow, the screens are so much more detailed and consistent than the ones above! And then the cave is different again, bland background and tiles, but many details scattered around... etc. Similar problems are present elsewhere in the level.
Still, like I said, quite OK for a first level and hoping to see more levels from you.