I've seen some statements that because all the stages were reworked, if we are going to get another character who needs every stage to be updated, this pass would be the time.
I cannot say if that's true or not, but if it happens to be... I no longer think my idea would take too much work. You start as Eevee, and he is able to evolve once per life, for final, into one of his 8 evolved forms.
- STAT CHANGES: Think of this like Shulk's Monado arts, except it's a permanent transformation, until you die. All of them have stronger special attacks (because they are currently all Special Attack stat bearers- we could get stronger Smash attacks if we get a new Eeveelution that has stronger Physical attacks). Jolteon would also be much faster than the other Eeveelutions. Umbreon and Sylveon would both have the best special defense/Defense against others' specials. Leafeon would have the highest Defense/Defense against others' smash moves. Etc.
- ATTACK CHANGES: Whereas Eevee might have a Sand Attack, the Eeveeltions would instead have firespin(Flareon), or Pin Missle (Jolteon). A take down from Eevee could turn into an Ice Fang (Glaceon) or Draining Kiss (Sylveon). These may come with their own changes. The aforementioned firespin would rotate around the opponents, trapping them there for a few seconds.
- EVOLUTION: How do you evolve Eevee? Well, perhaps it would be hitting both L and R- but it could be something else. More importantly, NOT EVERY Eeveelution would be available at all times. For example, certain stages might dictate which ones are available, such as Vaporeon being definitely enabled on any water stage. There could be a mechanic related to time to indicate which Eeveelution you turned into. Ultimately, it would have to be a bit generic (because it would be unfair for pro matches for time of day in real life to determine evolution, as an example). However, the needed requirements would be based on the actual ideas of the franchise- time, location, friendship, happiness, tools available. There would be some sort of meter/avatar shown for Eevee to indicate based on where on the stage(location)/time into match (time) / opponent? (tools/stones) / what mode youre in (friendship) / damage given? (happiness). It would show you which Eeveelution you'd become if you decided to evolve right at that moment.
- OPTIONAL IDEA--- Special Trait: Each Evolution would have an ability. Just to throw out some ideas- Vaporeon would never drown, and would even turn invisible when in water (like how the anime did acid armor, combined with an ability of Swift Swim). Umbreon and Espeon would both be slightly stronger in a team environment (they both evolve from friendship), but they'd have additional abilities. Sylveon, as an example, would reflect "status" with it's magic bounce- so Jigglypuff would put itself to sleep instead of Espeon, Ivysaur's Poison Powder would damage it, and Robin's dark...thing, well, it would just not work. The Eeveelutions could also utilize a type advantage, with Vaporeon having resistance to water attacks (like its ability water absorb). This adds more complexity for competitive play, and more fun for players.
This covers a fan favorite, many new types, and many generations, with the ability to update as new Eeveelutions come out. It also represents one of the most important parts of Pokemon, Evolving. It also covers new aspects of the series such as the day/night cycle, abilities, strategy of who to choose, and the stats. It also brings back type advantage in a way that is actually fun and strategic.
If you like this, ask me about my Team Rocket concept- it would add more of the missing Pokemon elements, particularly the capturing mechanic.