As for me and which Eeveelution that I would want...it's got to be Dragon type to complete the "special" typings. Eevee would evolve with a new kind "Dragon Scale" that would be consumed.
Dragon please! I’m surprised they haven’t done one already. It’s like the most popular type there is and I think a dragon type one would be really cool.
To see any of them added would be cool. However I am most curious about the design of a bug type eeveeultion. Moth wings? Butterfly wings? Round and bulbus body? 6 legs? lol.
Poison-type to counter Sylveon because that thing is too overrated and needs to be put in its place lol I know steel is super effective too but poison is just way cooler and has more potential imo and who will counter Toxineon? Espeon. But thinking about it now, who counters Jolteon if its only weakness is ground? omg Jolteon is OP
Watch out people I'm about to go full nerd mode
Its name would be Toxineon, mono Poison-type (name origin: toxin as in poison/poisonous/venomous) This follows the naming trend with the other Eeveelution names: vapor, jolt, flare/flame, umbra, esper/ESP, leaf, glacier and sylph.
Classification: the Contamination Pokémon
Ability: Poison Touch (moves that directly contact foes may poison them)
Hidden Ability: Natural Cure (this is in reference that snake venom, while harmful, can also be used in medicine)
How to evolve Eevee into Toxineon? I thought of several ideas for this. Idea #1 is to raise Eevee until it has high friendship then level it up while it's inflicted with the poison/badly poisoned status condition. To get a Lv. 2 Toxineon after hatching yourself a Lv. 1 Eevee, here's an exploit: give it tons of haircuts/massages/happiness-raising consumable items and then let it hold a Toxic Orb, then give it a Rare Candy. Idea #2 is to let Eevee hold a Black Sludge, causing it to take damage every turn. After a set amount of turns Eevee will evolve into Toxineon because its unstable genetic structure causes it to "absorb the sludge into its own body" thus contaminating it. But you will lose the Black Sludge item as a result. Idea #3 would be to have Eevee get struck with a set amount of Poison-type moves. Basically, all these ideas involve you the Trainer exposing Eevee to all sorts of poison. But by doing this you are also strengthening it by building up its immune system (that's why it has a chance of shrugging off status ailments such as burn, paralysis, etc. with its hidden ability Natural Cure)
I wanted a Poison-type Eeveelution for the longest. I drew my own version of Toxineon on Microsoft paint waaay back when but I don't have that old PC anymore....
There's so many choice! Dragon would be amazing, but I'm unsure it would fit into this specific region? I see flying type or poison more of a chance of happening, but I could be wrong.
I would love to give some ideas to how each would evolve into the new typing:
Dragon: Dragon eggs are a big hype when it comes to dragons; so what if the new evolvution came from breeding an eevee that's holding a dragon item? Since dragon items, like dragon scale are hard to come by in most games when there's more pokemon that need it, I thought Eevee just holding it would be better.
Fighting: Now this is one of the typings I really can't see happening, because most fighting types are on two legs rather than four. But I guess if it did have to happen, giving it a black belt item and it leveling it up with it could evolve it?
Poision: I agree with LittleMissPanda, we need something to counter Syvleon and a Posion eevlution would be awesome! How to evolve it? Either two ways:
Let your Eevee hold toxic orb, and while in battle is has to be poisoned and levels up after the battle for Eevee to evolve into its poison type. You cannot heal Eevee, and the more stragetic way is for your Eevee's exp points be close to leveling up before you battle anything. This way is a lil tricky, but Poison is tricky to work with so you need a tricky way for eevee to evolve. The other way would be simply being in a specific area with trash bags or like a posion rock and leveling up in that general area.
Steel: Is another typing I kinda like the look of. Why we didn't get this typing in Sword and Shield, I will never know. But I can see Eevee steel typing being a very robotic creature, a gear around it's neck is constantly moving. Either giving eevee metal coat to eolve with or a specific new steel type stone for it to evolve into.
Rock/Ground: I don't see the need for single typing for this. This one is simple, give it hard stone to hold and evolves that way, or if there is a desert like area in this new region, it can only evolve here, as this is where ground and stone are connected.
Flying: I think using the oval stone here would be interesting, need a good happiness AND depending on it being night or day, there would be two versions of flying type. Might be thinking like Espeon and Umbreon, but I like the idea that one will evolve due to moonlight. Or even give it air mail to hold while leveling up. Do we still have mail items anymore?
Ghost: Another good one that wasn't sadly in Sword and Sheild. I think one interesting way to evolve it, would be that Eevee would be fainted, and you level it up with a rare candy.
Bug: This one I don't really have much of an idea, other than using Silver powder when level up?