>>50197792Leafeon and Glaceon evolve from stones introduced in different generations.
Sun and Moon Stones also don’t have a thematic type to them, unlike other stones.
Sun used to be exclusive just to Grass types, but Helioptile can evolve with one.
Moon never had a type theme.
Both Pokémon are connected to the sun and the moon, respectively.
It could also be Shiny or Dusk Stones, since they are the actual counterparts. One is a stone made of light, and the other a stone of darkness. Dawn Stone is Awakening Stone in Japanese, so it is not the counterpart to the Dusk Stone and its mechanics are different.
Dawn Stone is strictly for Pokémon who have gender specific evolutions, where they change into a different class and gain a new type based on that gender.
What they should do with Sylveon is make a Fairy Stone, and also require certain Fairy Pokémon to evolve from this stone.
