Pretty solid little prototype, you have a good base here. The grapple mechanic is really cool and could easily be the center of a really satisfying moveset if you decide to expand on this.
Few pointers:
- The game's visuals were really small on my screen and it made it hard to make out what was happening. For a pixel art game you generally want to turn on viewport stretching, so that the game gets scaled up cleanly when the window is resized instead of staying at the same scale and just getting a wider fov.
- The art could use a little reworking for clarity - I ran into some spikes at the start because I couldn't tell what they were at all, they looked like background objects. The enemies also blended into the background a little.
- Really appreciate that you took the time to add a few sound effects, they really help with making a small prototype like this feel like something more of an actual game. I think the landing sound effect could maybe use some work though, it does just sound like a kick drum right now :P
I also notice that you don't seem to have actually picked one of the themes...? At least, you didn't say which one you picked in your explanation, which makes it kind of impossible to rate on it.