I really wish that they would just retcon the Eeveelution methods. So many gimmicks and features are getting scrapped it'd be easier to just use stones.
Flareon = Fire Stone
Jolteon = Thunderstone
Vaporeon = Water Stone
Espeon = Sun Stone
Umbreon = Moon Stone
Leafeon = Leaf Stone
Sylveon = Shiny/Dawn Stone
The only hard one is Glaceon because none of them particularly pertain to Ice. It'd have to be the one that Sylveon doesn't use.
