>>31878736First it needs a good ability like Espeon's or Sylveon's. It could keep Eevee's Adaptability or give it another offensive oriented ability.
Then a wider movepool. Things like Flash Cannon, Energy Ball, Psyshock or even Ice Beam (so it would have something different form Megaman or Raikou) comes to mind.
And last GF should boost stats on eeveelutions. 130/110/95 and then 60's might be good for first/second gen but now they need better numbers. That boost should be slightly in the higher stats and increase in the smaller ones, without touching their most useless (Jolteon's Attack or Umbreon's Special Attack).
So everything besides its main gimmick: being a pure electric type, evolved from a unstable DNA doggo
