To be honest I'm not feeling it with a lot of this stuff.
Making large pixel pieces is a tough job, but I think one of the biggest flaws in your pieces are the outlines and somewhat of the shading.
Taking your Lugia for an example, you seem to have outlined every area in a single colour with no regard taken for any neighbouring colours - this is most noticable with the border between the top of the mouth and between the white body and the dark fins. Neither do any of the outlines change between the areas that are facing the light source and those that aren't. Pretty much all the outlines could do with bolder and more distinguishable colour, and maybe some tentative anti-aliasing - something that really helps out the larger your work becomes.
(Also, what's up with the colour saturation on Lugia? The shading keeps going from nearly complete gray to something that's a shade of purple.)
As for the shading, well, I'm not a fan of how you shaded Piplup at all. Trying to copy Sugimori's use of tones like that on a sprite results in it looking more like a blurry, unconvincing gradient rather than a sharp and defined shade. This again applies to Lugia - the legs in particular come off really weirdly.
