I love a pico-8 game! This game would be impressive even without your engine constraint, but considering it im even more impressed.
The art here was pretty, and the design of having one map with multiple starting points was actually a really clever way to add a bunch of replayability.
That being said, i didnt really enjoy how the character controlled. They felt very weighty and sluggish, which really hurt the overall gamefeel. I think you were also lacking coyote time, at least when jumping from ladders i'd often feel the input get eaten by the game.
That didnt ruin the overall package though, which i had a great time with, good job!