On the Pichu-Bellossom, the Pichu face looks kind of fat for the flowers on it. Maybe you should make them bigger. On the Lairon-Tyrannitar there's some checker-shading you might want to get rid of. Also, the face looks kind of like it doesn't fit. On the Espeon-Swellow, if it's intended to be a mix, you should add more Swellow in there. If it's not, it's very good, the only thing I'd suggest is to make the shading a bit smoother on the tail. On the Cleffa-Igglybuff, it looks weird with both of the hair things. Also the face looks a little small for the body. On the Espeon-Mew, there's some weird white pixels next to it. This was most likely a transperization error. On the mix itsely, I really like this one, the only crit I have is where you join Espeon's tail with Mew's tail, Mew's tail is slightly fatter, so it looks a little strange. On the Ampharos-Flygon, there's a lot of checker-shading, but I think it's there on purpose. It doesn't look very good, so I'd suggest removig it. The only other crit I have for that one is that the arm looks like it's halfway behind the tail, but that might be just because the hand is small. For the Ninetales-Articuno, it needs more Articuno in it. It's also got some checker-shading on the wings, and the mane thing has a weird outline. For the Umbreon, it's good except for the eyes. If you shaded the eyes, that would make it look a lot better. And last, but not least, Ash. His clothes look a bit dark, and the outline is choppy on the recolored parts. Most official sprites weren't made to be recolored, so you usually have to re-outline.
Overall, your sprites are very nice, I'm only being nit-picky to help you becaome a better spriter
.