I describe a legendary Pokemon as one that GameFreak has announced as a legendary. It's simple but effective.
I voted only Phione as a legendary from this list since he/she/it is the son/daughter/child of a legendary, and it just seems like it would be a legendary. Don't ask me to go into detail, you'd understand in my size thirteen shoes.
The rest are rare Pokemon that are mistaken as legendaries (mostly Rotom), though Lucario was thought to be one when it was first announced, before Rilou was.
I voted only Phione as a legendary from this list since he/she/it is the son/daughter/child of a legendary, and it just seems like it would be a legendary. Don't ask me to go into detail, you'd understand in my size thirteen shoes.
The rest are rare Pokemon that are mistaken as legendaries (mostly Rotom), though Lucario was thought to be one when it was first announced, before Rilou was.