I struggle with the grapple too, but when you have the " thing " it's pretty cool :p ( because you can move faster ). I really like the art and was confusing with the end !
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You may want to try collecting the cubes until a ring icon appears in the top right corner. That's how you can unlock the other endings.
I thought about changing this design choice because it would stop some people from seeing the other half of the game (and maybe get a bad impression of it too).
Thanks for letting me know!