Toastie pretty much covered everything I wanted to say here. Your shading could also use some work, since it appears you just use the same shading that the sprites already had before you spliced them. I would suggest using darker colors on places that are covered by other parts, like the tail on Pikarisu behind its head.
To get rid of the black backgrounds I would just save a Pokemon sprite sheet to your computer, and then when you need a certain Pokemon, just copy the Pokemon you want, paste it into the program you're using, and make the background transparent before you do anything to it. You could also get the sprite sheet, and then use transparent selection (if the program you're using has that. I'm assuming it does) to each of the parts you're using in the splice, then just make the white background on your sprite transparent after you finish. Believe me, it is SO much easier to do than how I explained it. I tend to ramble in and make no sense~
In your newest sprite I really like the Pokeball effect you did on your newest sprite. However, the sprite itself seems to be a bit jumbled and messy. It's good that you're trying to use many different parts and all, but the way you did it didn't turn out good. Before you start making your splice, think about what you want the final sprite to look like and, particularly in this case, if the parts would all fit onto the base. Shinx is a pretty small Pokemon, and I think Pollosinxgoneus would look better if you used less or smaller parts on it. Remember, unless you know what you're doing with your sprite, try using Pokemon that are similar. Using Pokemon that are almost the same in size, and aren't too different will make it easier for you to splice them. For example, mixing an Espeon with an Umbreon will be easier than mixing an Igglybuff with a Rayquaza, but that doesn't mean splicing different things together is impossible, just more difficult.
Sorry if I sounded mean, typed too much, or made no sense; I'm just trying to help you~