Custom Character Tutorial
(without external folder)

Requirements :
-reading Getting Started and Character Info
-rigging knowledge
-Maya, 3DS Max or Blender

It's the hardest tutorial because you can run into many problems
Note that this page may be incomplete at some parts but hey! I'm doing this freely
This page might encounter a lot of change, be aware of that. 

First, export the vanilla model of the character you want to replace (cxxH00.mdl BE SURE TO TAKE HOCKEY VERSION) in brawlcrate and import body_h.dae into Maya or 3DS Max (importing it in Blender distort armature rotations, try converting dae to fbx before importing in Blender, and compare kosi_jnt in Blender and in brawlcrate > body_h > bones > root > kosi_jnt)

Now import your 3D model and scale it to the same height and width of the vanilla character (about 1 meter), if you're using Blender you can change View > Clip Start to a tinier value as 0,1m or your character will disappear when zooming in

Maya Rigging Method

Delete your custom character armature and replace it with the vanilla character's one.

OR         

If your character is in V-pose you can also select both vanilla armature and model, and your custom character model then go to Skin and click on the square at the right of "Copy Skin"

Then, go to Skin and click on the square at the right of "Paint Skin Weights"
and compare your custom character bind skin with the vanilla one
(I suggest to open Maya twice, to have 2 windows)
Here the Paint Skin Weights settings, (picture soon, though it's default settings)
Mode : Paint
Paint Operation : Replace
Profile : [third, with a filled circle]
Weight Type : Skin Weights
Normalize Weights : Off
Opacity : 1
Value : 1
Use Color Ramp : True

Click on a bone name then hold click on your character like you're painting it.
you can hold B and left click to change the brush size

When you're done go to file > Game Exporter and export with Up axis Z as Binary FBX 2013
then import that fbx in Blender, export as dae and read the text after Blender video link below

Other 3D Modelers Rigging Method

You need to manage to get vanilla character armature over your custom one, as we can't edit animations.

The armature is also linked to triangles, you can change which triangle is assigned to which bone by checking the vanilla characters (look Characters Info for bone names)

Blender rigging YouTube video : https://www.youtube.com/watch?v=f2pTkW-1JkE

And                 
use those settings while importing in brawlcrate

after importing, check if box min values are between -2 and 0
and if box max values are between 0.1 and 2. if values are too tiny, scale up by 100 your model (It was always this factor for me)

Finishing your model

the model preview in BrawlCrate should be facing you. if not, change to -Y forward and Z up in Blender export settings (then rotate your model / check root bone settings if it's still not that, but make sure feet are on the ground, height ZERO, and don't edit any bone except root)

Go to Shader0 > Stage0 and replace MultiplyBy4 by MultiplyBy1

then either copy and paste your model body_m and body_l or make now poly versions used when the character is far away from the camera. Copying body_h didn't cause any lag to me
for body_s, you can keep original one if it's a reskin of the character                                           
(C and B versions are same but H has hockey stick shadow)                                                         
or you can :                                                                                                                                          
- keep the vanilla one and go to materials and replace cull_inside by cull_all

- put an empty model with the armature                                                                         
                
- copy your lowest poly character over it / make a single material version of your character and replace Shader0 by this and all materials by this (delete texture references)                 

keep light.tex0 for cxxH00.mdl        for other versions you can delete it

You can also delete env00.tex0, micon.tex0,  _a and _sp textures and the two last eyes PAT animations + textures (or all if you don't plan to use eye animations, by the way, if you plan, rename the eye material like the vanilla name (something like "cxx_eye_mat"), the eye textures like the vanilla name (cxxeye_00) and remove all "Texture1" from PAT animations.)
purging your character file size by removing unused stuff purge also the RAM :)

I guess you know how to replace your character over cxxH00.mdl and that you just have to delete the hockey stick models and textures to make cxxC00.mdl

for cxxB00.mdl then add env01.tex0 (same for every character)
and add bstick.mdl0 (not the same size for every character, imagine Bowser using Toad stick. You have to export bstick.mdl0 from the vanilla character you're replacing. )
if you want a custom hockey stick color when fighting behemoth, go to materials and click on Color0 box then on the arrow at the right.

Then, for menu.mdl, delete cicon.tex0 and all models except body_h.
Save and let this file as a brres.

I highly recommend making two filesystems : one vanilla, and one modded (if you plan to do more than 1 mod)

I also recommend running a decompressed Mario Sports Mix Filesystem through dolphin by double-clicking main.dol in sys folder