For starters, I already expect you to have a skeleton built. It's pretty easy to make one, it's just a matter of finding the bone tool in your modeling program. If you're using an existing one you imported from a brawl character, simply resize each bone until they match the proportions of your character. At the start, you should have something like this:
Next, you're going to select your character and add the skin modifier to it. If your character is made up of separate objects, add the skin modifier to each of the objects. Remember, once you rig your character you can no longer edit the mesh. Doing so will cause all of your bone influences to be set to 0 in most cases, meaning all of your work will be reset. (Heck, even once during this tutorial I did this by accident and ended up having to redo an arm. This is why you should SAVE OFTEN!) Next, you're going to go into your skin modifier and add every single bone in the scene to the list, so that every bone influences your mesh. If you try to move the skeleton at this point, you will notice that it may work relatively well, but there might be some vertices left behind, strange deformations (especially in the arms and legs), or bones affecting vertices they aren't supposed to. This is where the main bulk of the work comes from - weighting the mesh. The first thing you're going to want to do is shift your focus to one area of the model at a time. I started with the head.
Here we see that there's some vertex stretching on the back of the head. To fix this, we have to make sure that these vertices are 100% weighted to the head bone. This will not always be the case, as you will see for the arms, which has varying influences throughout. For now let's fix the head.
With the Envelope subtab selected under the Skin modifier, you will notice a box labeled Select at the right of the screen. Check the "Vertices" box, as seen at the right side of the picture above. This will allow you to select the vertices of the mesh individually, so that you can begin weighting them. You'll probably always want to have this box checked. Next, select the problem vertices. Now open up the weight tool by clicking the wrench, as indicated in this picture:
Since these vertices are only supposed to be affected by the head bone, we select the head bone (or in my case Bone04) in the list at the side and we click the square labeled "1" to set the weight to it's maximum of "1.0". (Notice those 2 pairs of "+" and "-" buttons? The top pair is going to be your most useful tool for tweaking the influence of the bones, specifically for the limbs.)
Now that we've done that, no matter how much the other bones move, these vertices will not be affected by anything but the movement of our head bone. That was easy!
The real challenge comes from tweaking the other bones (mainly the spine and the limbs) to deform naturally. Now that you know the basics of what it is we're doin', next I'm going to show you the basics of weighting an elbow, as well as show you some problems to look out for during the process.
First off, bend the arm at the elbow.
Notice how the arm's width on my model is smaller now that I bent the elbow? This deformation is exactly what we need to fix if we want natural looking animations. Remember that pair of "+" and "-" buttons I talked about? Well these are going to be crucial for making this elbow bend correctly. (It probably would have been better if I made a video for this part, but I'll try to keep this moving along as best as I can.) As a general rule, the vertices the elbow will be bending at are going to be weighted heavily to the upper arm bone so that they do not move with the forearm bone. Depending on your character's proportions, this might cause some clipping, but this can either be completely fixed through some tweaking or at the very least it'll look a lot better than the arm caving in on itself. The vertices on the opposite side of "the bending edge" are the ones that will receive a mixed influence of the two bones so that the width is maintained. (In other words, the vertices towards the back of the elbow will be split between the two bones, while the vertices towards the front of the elbow will move as little as possible by being attached to the forearm only.) It's not as hard as you might think, but it does take a lot of patience, and you do sort of have to eyeball it. Here's what you're aiming for:
Again, those vertices towards the right of the screen are the ones that have close to 0.5 influence for the two bones, but the influence of the forearm gradients out as it gets towards the vertices at the bend.
You should see very little change in size as you bend the elbow back and forth. The legs are generally the same, but since they are usually close together, one leg's bones may affect the other leg as well. To fix this, you simply have to set the influence of the opposing leg to 0 for each.
(That'll probably make a lot more sense when you see it happen
)
The spine is generally very straight forward, and I doubt you'll have much trouble with it, as compared to the limbs. When you think you are finished, it is important to drag the root bone (or the bone that has influence over everything, usually located near the pelvis) pretty far in one direction to make sure there are no vertices that are not assigned to a bone.
Finally, it's important that you put your character in a lot of extreme poses to see where the rig doesn't hold up. Since you're reading this you're probably the rigger as well as the animator, and it's important you know that your animations will not be as fluid as you want if you're always having to animate around the problems with your rig. If you're importing your character over an existing brawl fighter then this is especially true since the characters have already been animated without the weaknesses of your rig being considered, so be patient and be thorough.
Good luck!
