smash bros waifu rules following December 7
1. If a female spirit inhabits a male character then that female spirit's physical characteristics overtakes the character and they transform into an amagimation similar to bowsette.
2. If the female spirit revered as a top quality waifu possess the body of a female character then their personality will shine through but the character will keep their physical characteristic. Ex shante and samus
3. If a ship is made better by the spirit then go for it. Ex Pauline's spirit inside Peach
4. If you use the rabbid spirits you are below humanity and natural selection is coming to purge you. Ex Rabbid Peach in fem Robin

These are not set in stone rules but guidelines to help you. So be safe and smash as well as spirit responsibly