I'd love it if you could include the palette used in each asset. With the palette shaders can be made to recolor the assets like how arcade games did it, by replacing each color with a new one.
This would make it easier to make dark palettes for caves or sewers, or night time colors, or even Player 2 color variants.
I love the work so far and would love to do something with Ruin Runners and Shaia... I will need to come up with some ideas
Edit: I didn't realize these were palettized PNG format. Awesome!