>>23202985Manaphy and Phione both don't qualify. There can easily exist more than one of them and they don't have anything special about them.
Lugia, Ho-Oh, Groudon, Kyogre, Rayquaza, Dialga, Palkia, Giratina, Arceus, Reshiram, Zekrom, Kyurem, Xerneas, Yveltal, Zygarde and Hoopa are actually powerful mythical beings. Lesser ones like the birds, the beasts, the golems, the spirits and the swords are a different category altogether.