I don't recall how this level was like before, so take that in mind.
there are few spots where I would have done tiling differently (eg. pipe and teleport, bars aren't connected to the ceiling, ground edges around lava). but that's just a nitpick. overall, it's fine.
I'm not 100% sure on those checkpoints, either. in the green key area, I would put a checkpoint right after the player collects a key. on your first play-through, after you leave the pipe, you might not know what's over there and just grab the save point. if you don't already know this level and save it for later (when you actually own the key), the checkpoint is practically useless.
I did, however, enjoyed this sandbox quite a bit. the enemies were fairly placed without being pushovers. jumping on moving platform was fun. disappearing ones can be a little annoying, but you used them well. it's a sizable area but the directions are clear so I never got lost. I like the pipe shortcut in the middle of the stage, that's a nice addition.
overall, good level.
