Very clever, finally managed to beat it with 2 gems remaining! Curious to know what's the most efficient path and how many gems you can keep in the end. As some other people already pointed out a faster undo would be really handy and I would also like to point out that I found some secret walls that are probably unintentional(Room 0: to the right of the door; Room 3: in the two bottom corridors; Room 7: in the rightmost wall).
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Thanks for playing~ i managed to beat it with 16 gems remaining. but with faster undo (and the fast travel trick) i can do 43 - ah yes, some of the secret walls are unintentional - i couldve changed the tile to a different color to test it beforehand (the intentional ones are: room 0 right door was intentional as that get you to the "black" key, one connecting between room 0 (left) to room 2 and one on room 4 to get to the black tile)