Glad you enjoyed!
1. Mm, I'm still working on striking a balance with difficulty. It's a learning process, especially as I keep refining my combat system.
2. If the game had art commissioned for it, it wouldn't have been free. What you suggest (potentially) for the inclusion of Enemies would bring us up to 15-16 pieces of unique artwork alone.
3. I've since improved how I handle maps in future games, in that they're now connected spaces rather than individually floating rooms. It helps!
A patreon is something I'm eternally considering on-and-off. Charging for MERCANOID now would leave a sour taste in my mouth, but not all future projects will be free, no. As my quality grows, I'll be more confident in charging for a game, allowing these older titles (and occasional free smaller projects) serve as my demos.