I went to the right to the islands and pull both levers here. I stuck in cave tunnel. I exploded bomb in lava/magma and it just got all yellow and still killing me if I jump into it, maybe I'm just played dumb here and waste bomb :/
About sound effect: well, idk, maybe it gives the game a distinctive thing but you should make it not jump sound, maybe some graphics feature or maybe phrase when you jump like "eoeoh" of something :D
About checkpoints and dying: yeah I saw when you die you dont lose any progress - that's good, well actually not ideal: box teleport to its original place, but I think it's because you want player to not lose it somehow
Thanks for your detailed reply! I'd like to finish the game and see all of the content