I played the game twice, the first time on my phone and the second time on my PC. It's really awesome! I love the mechanic, the atmosphere, the lighting, the sound design and it just looks so polished! I read comments saying they would like more hints. I find it especially great to study the shadows, guessing whether I will launch myself into some spikes or make a safe landing. So, if you're going to work on this game as a full version (which I could totally envision), then maybe let the player choose by implementing different difficulties. But for this jam, you crushed it! Only the theme is not really followed ;)
Edit: I wanted to say that on mobile it's way harder to guess the shadows right and also the aiming is pretty tough. Like another commenter suggested, it would be great to have an aiming mechanic, e.g. hold left mouse button / finger to show the line and/or anchor point and on release, actually launch the grappling hook. Could be combined with some assistance (indicators for spikes, etc).