Splices
Splicing is when you splice together parts of two Pokémon sprites. There are really three types of splicing. When "adding parts", you're for example making a Pikachu with wings - you take a Pikachu, put wings on it, and then you have a sprite of a Pikachu with wings. When "mixing", you're maybe taking a Scyther and a Butterfree, and mixing them into one Scytherfree which has features from both, something you could picture as being the result of crossbreeding them. Basically, when adding parts, you are deliberately aiming for the result to look like one of the Pokémon you used with something added on it; when mixing, you should try to make it look equally like both. Then there's the "supersplice" in which you're not aiming for your Pokémon to look like any of the parts used. Generally, supersplices are spliced from a very large amount of parts, with pretty much one Pokémon for the body, one for the front legs, one for the back legs, one for the head shape, one for the muzzle, one for the ears, et cetera. They usually have a lot of scratch parts and edits, and I don't recommend doing them until you have quite a bit of experience in the field of mixing and adding parts.
The Rules of Splicing
Do NOT copy-flip. Copy-flipping is basically when, say, you put on one of Charizard's wings, and then you flip that wing and use it as the other wing too. As I said, don't.
DO flip parts if they are facing in one direction and your sprite is facing in the other.
DO recolor the end result to one color scheme.
DO edit the shading style to make sure all of the body parts colored with the same color match. This also applies if you've flipped any parts - you'll need to change the direction of the light source.
DO add in parts from scratch if some of a body part you're using was obscured on the original sprite but will not be on the splice.
Now, how do we splice?
Firstly, you need to get the sprites into your paint program, obviously. You might want to use both R/S and FR/LG sprites, maybe even Emerald ones or ones you've revamped (but ONLY if you can honestly look at your revamp and the official sprite side by side and not tell which is which except for recognizing the pose). Here, I'm going to do an Electabuzz/Aerodactyl splice (generated by the random Pokémon generator), I'm going to use the FR/LG sprites for it, and I may use parts from my revamped Gold version sprite, so I'm opening that too for safety. For now I can't be bothered to use the R/S sprites or anything too. [screenshot]
Now, decide which parts you want to use for the splice. I have decided that I want Electabuzz's little antennae, the hair on its head, the markings, probably the sides of the head, the end of the tail, the claws, and the arms, while keeping everything on Aerodactyl except the end of the tail and the horns. Then remove everything you're not going to use - just erase it carefully, making sure to remove everything you were going to remove and nothing you weren't going to remove. Don't do it if the part is covering up some of an area you're going to use, though - you can erase what's not covering it, but keep the exact part that's covering it intact. Again, for safety, if you're using many sprites from different games, erase those parts from all of the different sprites. Now, in my case, even though the markings and sides of the head are probably going to be drawn on Aerodactyl itself, I'll still need the sprites for reference, so I'm not erasing any of them, but note that in Paint, I highly recommend just making extra copies of the sprites if you want reference and erasing from the original copies, because in Paint, the lasso tool is not very precise and therefore it's very hard to select what you want completely but without any extra pixels.
Now you should have all the parts for your splice ready. [screenshot]
Next, select the parts with the lasso tool [screenshot] and get them onto each other. In Paint, you have to drag the part you want to be in front onto the part that you want behind. In a layered paint program, you can just copy the parts, paste them into the other image, and then drag it around independently and switch the order of the layers. Place the parts carefully - if you're putting on a new tail, don't make it come out of the back unless you're intentionally making a freaky splice. Don't mind the gaps that may be left in there somewhere - placing the parts so that the sprite looks right is more important than leaving no gaps, because you'll fill them in anyway. Now we have the first version of our Aerobuzz, the way some *cough* spriters would leave it - you don't really need to see the Electabuzz anymore, so no more screenshots:
But we're not just some spriters. After you're satisfied with the overall image of your sprite, you can start filling in the gaps - from scratch. Basically, you draw in any missing parts pixel by pixel with the pencil tool, and make carefully sure to shade them - see the revamping part, which you should have read, on shading both body and outlines. Usually these parts will be small; if they aren't, I suggest you change your plans for the splice until you're a bit more experienced. In my case, it's mainly the right (our left) arm, but I'm also erasing a pixel from the tail end that looked odd, and don't forget to edit out the parts that you weren't going to use but were on top of some you were going to use.
Anyway, when you've drawn those in, it's time to recolor. When mixing, you'll usually want to use the colors of the sprite that's less prominent in the mix as it is so far - which is almost always the accessory Pokémon rather than the base. In this case, that would be Electabuzz, and I've already assumed that with my plan to give it Electabuzz's markings. When adding parts, you'll on the other hand want to use the colors of the base, since the desired effect is not to make it look like both of the Pokémon spliced. For supersplices, the colors are often taken from a completely different Pokémon or made up (see the recoloring part of this guide).
But as I said, this is a mix we're talking about, and therefore we're going to recolor it with Electabuzz's colors. We do that exactly as we'd have done it if we were simply recoloring a normal sprite to another color. (i.e. go read that recoloring guide if you haven't already. Now.)
But no, no, no, don't stop yet, even if you have no plans to start putting on markings. There may be slight oddities in the shading now - maybe you flipped a part so now the shading is backwards, or you put a part somewhere and now it would cast a shadow onto the rest of the body, or a part used to be shadowed by another body part but isn't anymore. Additionally, the shading style might be different between the Pokémon that you used - one might then look darker than the other (see the revamping guide). Therefore, you might want to change the shading a bit to fit better in your splice. I'm going to edit the outlines and take out some pesky Dots, but you don't need to if you don't want to - they're official flaws, after all.
Now, since I was going to use the markings, I'm adding them on. Obviously, I need to adapt them to the surface of Aerodactyl's body, and shade them like on Electabuzz. This is probably the hardest part of this particular splice. When working in a layered paint program, I highly recommend putting markings and such on a new layer. Oh, and I changed the claws into Electabuzz-like claws, as I intended.
Now our Aerobuzz is ready to roll!
Adding parts and supersplicing will not be specially covered here, but the method is the same - only real difference is how you end up coloring it. Have fun splicing.
Beware, she double dips!