I want to improve spriting and am looking for constructive criticism

[Sketchasaurus]

It seems as though you're shrinking down and cleaning up the card art of the Digimon for these sprites.
One issue I see, particularly on Alphamon, is that there is very low contrast between shades and a lot of the linework kind of confuses details together a bit. I definitely recommend checking out the Digimon Battle Spirit sprites (and the ones from Battle Spirit 1.5 on the wonderswan) to get an idea of how to approach Digimon sprites at this resolution.

I cooked up an example of what you can do by referencing from Gallantmon (the yellows and red were borrowed from those sprites)