You should use more reference while spriting. Even if they are full custom, using real pokemon sprite as reference isn't consider splicing and will really improve you sprite. Specially since you now have 649 sprites to help you and even more if you take each gen sprites. You purple pig bat could use more Woobat as reference to help you to make it cleaner.
There is often shade missing which make them look sort of plain and sometime boring. Not because they aren't nice, but because they look more like WIP then finished sprites.
I think your main spriting problem is your lines. Many don't look clean. Maybe due to shading or I don't know, but not clean.
As for your old one, I think using reference is VERY important with fire because it easily look wrong. Rapidash, Magmar, well any pokemon with fire on it is a good ref and you'll see the difference between those and your fire and how your look stoic instead of freely moving.
I only point negative thing, not because I think your a bad spriters, but because I think it's the best way to improve. It wasn't meant to be harsh if you ever considered it that way.