How to edit vanilla characters

[MarioFaker]

I want to make a mod where I edit the abilities and stats of sonic but I don’t know how to do that.I have been using SLADE but that hasn’t worked so if someone could me out that would be good.
(By the way I’m not trying to make a new character slot in game)

 

[SonikkuBoy]

take sonic's S_SKIN, rename it P_SKIN, and edit what you want

 

[rosie the racoon]

should you edit tails' s_skin / P_skin to edit him