very nice detail work and enemy design! the second and last rows are the type of creatures I would want to catch.
when working with pixels, its best to avoid using tweening imo. it works with these because the images are big and you don't really see the pixels when they're zoomed out, but that sort of defeats the purpose of pixels. rotation is okay, but it still does crunchify the image. also, with pixel art, less is more. when moving from normal digital art to pixels a common mistake, and one that i still struggle personally with is making the canvas too big. even 100x100 takes up most of the height on a gameboy advance screen, which still impresses me.
all of this advice is only relevant for if you want to emulate retro stuff though. hope it helps!