I know this is a prototype, but I think your name could be more expressive of the content I'm going to experience. Names are an essential way we interact with media, and coming up with even a functional name ("Multiplayer Stealth Coin Game") is valuable design work, which will give your audience a good idea of what you're trying to convey, and internally give you a way of referring to the game without "ownership" - "this is XX's prototype". I'd challenge you to come up with a more creative name that just a functional one.
The UI/UX design of this game is lacking, which is fine, because it's a prototype. However, you have a responsibility as a designer to communicate to your testers/team how to play the game, what the goals are, and what is missing that you wish was in the game. After playing the game and beginning to give feedback, I saw a comment you posted that said "Coins randomly appear throughout the map, move with (WASD, IJKL) and Sword attack with (E, O). Collect coins and use (1234, 6789) to change color." -> however, a) this isn't where itch game instructions are usually placed, and b) it doesn't show / explain any of your design decisions or player goals. I would challenge you to consider your presentation and aim to communicate them better, as the quality of your feedback depends on it.
Resource wise, I think attacking could use up the resources you have, making it impossible to hide any longer in that color?