Characters info

Assuming you've already read Filesystem/chr and ID LISTS to know which file to edit

about models

Bones names are just real body parts in japanese

L_ and R_ before the name indicates Left or Right

This is in kosi_jnt :
                              eff_hip = hip
                         momo_jnt = thigh
                           sune_jnt = knee / body part above feet
                               asi_jnt = feet
This is in mune_jnt :
                             kubi_jnt = head
                           kuchi_jnt = mouth
                                   kata = shoulder
                              ude_jnt = arm
                                hiji_jnt = elbow
                                 te_jnt = hand
                                tekubi = wrist
                                   yubi = finger
                                   stick = hockey stick
                            mimi_jnt = ear (used for moogle)
                        p_food_jnt = hood (used for White Mage)

                         shippo_jnt = tail

                                   shita = tongue

about textures

If you just want to edit a texture, do it with Yosh's python script / Yosh's discord bot on the discord server, 
or else BrawlBox will distort the character and you won't be able to save it if it has an external folder.

and one (Ice Luigi) done with hex editor or Yosh's python script

about PAT animations

in every character file, the game tries to load optional PAT animations to animate eyes (it doesn't crash if they are not there).
Their name refers to the material name (change the eye material name to the vanilla one if you want animations to work)

below a list of every PAT animations + their use (invert the two last digits for texture name) :

cXX_eye00 (textures cXX_eye00, cXX_eye01 and cXX_eye02) - blinking

cXX_eye01 - angry

cXX_eye02 - sad

cXX_eye03 - happy

cXX_eye04 -  damage

cXX_eye05 - unused tired face

cXX_eye06 - unused sleeping face

after special tests with a custom Mario, here's when those animations are played

-opponent score a point
-match ends on a draw (also on result screen)
-losing a match (also on result screen)
-going in jail in dodgeball
-failing a charge attack during face off (hockey)
-losing in harmony hustle

Happy when :
-scoring (except in hockey)
-posing in the VS screen
-team cry (after presenting characters)
-an opponent fall into water on DK dock
-winning a match except in hockey (happy on the result screen even in hockey)
-killing someone in dodgeball / hitting it when in jail
-you're on the ground after your opponent became ninja in star cup
-victory text appears after you've beaten behemoth
-you put the tournament crystal on starship

Damaged when :
-getting hit by items (except minishroom)
-losing the ball (or a fruit)
-getting hit by stage things (Waluigi pinball, dry bones, podoboo...)
-opponent attacks you
-getting hit in dodgeball / Bob-omb dodge (by players and bombs)
-you jump after scoring in hockey (when you touch the ground you're normal) -opponent gets transformed into ninja in star cup (when you fall off until you touch the ground)
-ninja steal the star cup
-there is a black hole (you're on the ship before fighting behemoth)
-you're KO

you can also read How to make a Texture Hack (with a python script Yosh made)

(works for every 3D model in the game, including stages)