I made my first climb to Master Ball using an Eeveelution team
I was able to hit Master Ball doubles with an all Eeveelution team. Pokemon Champions is my first time ever playing on the ladder in any of the games, so I'm pretty happy to make it to Master Ball. And it was fun to do it with this theme team. But it does have some major limitations such as no mega, no fake out, no tailwind, and no reliable trick room setter.
Sylveon - Surprising nobody, Sylveon is the heavy hitter here with standard pixelate/fairy feather build. The major difference is Round is here for one of the few forms of speed control available. Choice scarf Espeon clicks Round first, letting Sylveon go next with with a doubled 120 bp fairy-type Round with two 1.2x multipliers on top. That double up eliminates most things that don't resist fairy, including taking out sash Aerodactyl and Pelipper before tailwind gets set up. Just Sylveon's follow-up is an OHKO on most Archaludons, which is only neutral damage. The other dragons don't stand a chance
Espeon - Other than enabling Sylveon with Round, Espeon is the Charizard Y answer, outspeeding it and taking the OHKO with a 4x effective Power Gem that noone expects. If ZardY has Whimsicott tailwind support, Espeon just barely survives heat wave (but not weather ball) and revenge KOs Zard. Psychic gives you STAB effective into stuff like Sneasler, Venusaur, Gengar. And Alluring Voice can help clean up against dragons, usually for neutral into Arch, in late game if not already scarf locked.
Jolteon - This is the only other speed control I've got and Jolteon put in a lot of work with the focus sash and Electroweb (aka Electromiss from my experience). Jolteon is the secondary Sylveon Round enabler. Helping Hand and Thunderbolt are the last 2 slots. I considered fake tears, but went with helping hand for situations where Jolteon would be knocked out first. Also figured it would help out Leafeon and even Umbreon Foul Play. Neither of which ever happened.
Umbreon - My one and only fake out immunity and a lot of people forget that. Taunt on Umbreon was also my answer to trick room teams. It's also nice that you can leave Sableye useless after 1 turn, since it's non-prankster taunt. Otherwise, normal bulky annoyer support with snarl and yawn. And Foul Play is the best answer I have against Basculegion with swift swim or tailwind active.
Leafeon - The official bench warmer. Not kidding, I brought it to one match and it didn't see the field because Espeon/Sylveon swept. Originally thought about having Sunny Day on Jolteon for Cholorphyl, but there were too many more important moves. Maybe drop Thunderbolt on Jolteon, but then all its moves hit like a wet noodle. But for real, drop Leafeon from the team and try Glaceon if you want. Sorry Leafeon (and Flareon) fans.
Vaporeon - I was surprised at how often I ended up bringing Vaporeon. I saw a LOT of Incin, Garchomp, Dragonite, Dragapult, Excadrill and it does well into those. It's a good switch into fire and steel types. And getting healed switching into a Jet Punch, Aqua Jet, Wave Crash, etc., and healing is fantastic. Vaporeon also does bulky yawn support like Umbreon, but with detect to make the most of leftovers healing and to ensure you survive until the sleep turns.
And that's the team. Code's there in case you want to try it. But I would probably recommend against it. Trust me. But let me know if you guys got anything cooking for Leafeon or Glaceon because this was basically a 5-man team.