Well, you said you'd like constructive criticism, so I've decided to throw in my two cents. Figured I'd take your three most recent splices.
Ivysaur+Croconaw, I find it to be lacking with Ivysaur. The grass and bulb are hard to make out as a bulb. Beyond that I don't have much to say, really just looks like a recolor more than anything. Perhaps using Ivysaur as the base may have yielded a better result. Perhaps adding things like Ivysaur's ears or pattern might have also been a good option.
Scyther+Victreebell, the first thing I noticed is that it seems really weird when looking at it from afar. It just looks very unshaded, this is probably due to the lack of contrast in the shaes you chose. I realize that you probably just took the shades one by one in order, but it may have been wiser to be a little more choosey in which you put where. The lighter shade could have been used for the general color. Next up I'd have to say I think the leaf is a bit choppy and looks in general not very good. Missing its boarder in a bunch of spot, and just in general looks a bit too cut up. The Green segments between body parts should probably have a green border instead of brown ones, or even still maybe a brown color may have looked good for those. The tail again is another example of bad placement, as it's hard to see. I think maybe the spotted patter would have been a nice extra touch too on Scyther's body.
Venasaur+Ninetails+Dragonair+Snorlax+Clefairy+Pidgeot, wing mirroring and stuff they say is a bad thing. You have to be careful when doing it. Things like shading need to be fixed, and the way you have it, the wings don't look like they are placed correctly. Really they should be connecting at ti's spin, yet the way they are the body it looks like they are kind of tacked onto its side. You missed some brown pixels on the tail. The pink part has the aqua colored boarder. The horn seems to come out at a weird angle. I don't like the giant blotch of boarder color where the tails meet.
I hope this can help you out in some way. You have some potential, and really just need some proper refinement and attention to detail to really advance.