So.. I plan on publishing this as just a bunch of mostly plain text just so something exists, I Probably won't ever make this any better, and I might just abandon this if I drop Vex or something but I feel more or less confident that I like her as my primary mid pick, so who knows, maybe this will look good?

Anyway, genuine apologies for a wall of text, I promise if I put time into this I'll actually format it.

I'm not good at this game in any sense but I've seen that there are like... no vex builds available? Like all of them are from season 13 and it's really annoying so I'm gonna do... something about it ig? again, I am literally an Iron player right now so I don't know much of anything but something is better than nothing I guess, right?

I plan on sticking to what I know works, I'm not gonna plug my insane spellbook Vex Hullbreaker build, so don't worry about that.

I just did the runes, I hope to do the items and Summoners soon, but I honestly may wait until 14.2 to do so.

Specifically it seems like Electrocute and Dark Harvest are the two keystones you have a choice over. I don't really think keystones like Summon Aery or Arcane Comet fit well with a burst playstyle and everything else seems worse than the 4 (I haveen't tested and will sure try when I feel like doing funny things in unrated).

The Chapter below this one is a long-inded rant about whether you choose Electrocute or Dark Harvest.

I put a TL;DR there but here is another:

Choose Electrocute most of the time, especially if you're new or not confident in your own skills or the matchup.
If you feel confident or you're in an easy lane (Sorry, I have not played this character enough to say who those are really) AND YOU ROAM YOU NEED TO ROAM, then Dark Harvest can make for a great snowball build.

...So, if the choice is between Dark Harvest and Electrocute...

TL;DR: I personally think that Electrocute is the better rune in the majority of situations!!!

Dark harvest feels like it would work very well with her kit and her ult's refresh, but I feel DH makes you lose a lot of the potential you have to be an absolutely obnoxious early-game bully. DH has twice the cooldown in a 1v1 and it's damage is only going to stay the same as long as you're consistently stacking it. If you don't the damage will fall behind.

BUT.

If you DO manage to farm your laner and roam and get some off of top and bot, then you can give yourself a rather disgusting snowball and the ability to proc DH on multiple enemies with your ult combo in a single fight.

Now that I got that out of the way.

For now I'm assuming your primary is only Domination. If I find cool stuff for another catagory I'll make one for that too.

For now I guess I'll just do the row and the best rune, and state alternatives

Malice: Cheap Shot
Cheap Shot is pretty clearly the best rune out of the three, you are going to be fearing your opponents pretty frequently and also getting easy follow-ups, so you'll see this doing a lot of damage especially in laning phase. I don't think ToB gives you nearly enough healing to be worth it in midlane where you're taking burst damage instead of getting poked 90% of the time.

Tracking: Eyeball Collection
You're an assassain and an aggressive one at that, Eyeball Collection is the easy choice. If you feel like you won't be able to roam, however (which is really bad for you btw), Ghost Poro is the best alternative.

Hunter: Ultimate Hunter
This one is by far the most set in stone, Vex's Shadow Surge is an incredible ability for many reasons I'll explain later and so any opportunity to do it more is in your best interest always.

SECONDARY RUNES

(I'm currently trying to find a way to get resolve runes in here, if you're curious I'm looking at Demolish, Shield Bash, and Unflinching)

For now there's just Sorcery:

Manaflow Band: I feel like I have trouble with running out of mana on Vex, even when I'm hitting most of her abilities. I feel like Manaflow lets you keep on bullying in the earlygame and lets you not worry too much about not having enough to burst someone down.

Scorch: Again, this exists to help you out in the earlygame. Just a little extra damage to keep you in the lead a little.

Transcendence: Extra Ability Haste means more Ulting and comboing. The final passive is also pretty tempting, but I feel like it isn't quite as good as scorch, but I'll keep you updated, for now I would take Scorch as a safety net for laning phase, though.

I think Gathering Storm is bad: I just didn't want to include runes I didn't think worked but I think Gathering Storm can look tempting, so I want to definitively shoot it down. Vex, along with most assassains, plays best in the mid-game and begins to fall off during the late game as the other characters get enough armor to survive your burst and just kill you. GS is only really good after 30 minutes and at that point you really want the game to be ending, it won't do you any help before that.