Yeah, it's kinda like Kid Dracula. Really enjoyed it https://cobaltaoi.itch.io/the-boy-and-the-mysterious-amulets
A GBC version sounds really interesting, looking forward to it. Regarding difficulty I think you could perhaps do what Bloodstained did, and have a sort of classicvania mode difficulty. If you fall into a pit or spikes you now lose a life, there's knockback, etc.
As for the hitboxes they're pretty fine anyway, you'd only want some minor QoL adjustments here and there.
Also, no problem and good luck with the post-jam version!