Thank you so much for the kind review and comment, we're so glad that you enjoyed our game and its song :D
There are no indications on what you can grapple because you can grapple literally anything, even the ground! Pro tip: if you grapple the ground, it'll give you a slight speed boost ;)
Balancing the time was a hard task indeed, and we wanted to add a "free roam" option in the menu, to let the player explore the level however they like, and get used to how to reach certain places, but we didn't get enough time unfortunately :(