The idea is really original. I like it.
- Taking it a bit further would be cool. Allowing both the diver and the submarine to move could make for some nice challenges.
- The player hitbox is really big so navigating is quite problematic.
- Also adding more lights could help guide the player where to go.
- The art doesn't match pixel wise (player's pixels are larger than submarine's pixels). It's dark so it wasn't a noticable issue anyways.
That's a lot of criticism that I'm giving you, but I think that this game has some potential if you would like to explore it afterwards. Good job!