Steve aka Alice, Harrington in the future Hopper
Stuck in the uspide down since he's 11 (1977)
El managed to make a mini opening portal, years way before 83, in 77 which led to Steve getting caught in and being stuck in the uspide down.
He was reading his favorite book Alice in Wonderland when it happened, and so he named this world after that book, as a way of adapting to his trauma.
After falling he started living there, He settled near the lake. He's slightly more childlike and crazy, since he hasn't had any contact with other humans since he was 11 years old, and was stuck in this crazy world for 7 years.
What happens is Will is drawn to Wonderland in 83, 6 years after Steve. They meet, after Steve saves him from tweedle dee, and introduces himself under the name of Alice. Another way he coped with his trauma, and also because he ended up almost forgetting his name.
Later, Will is saved, but not Steve who was creating a diversion so that Will could escape.
The rest unfolds as in the canon, except that Will spends his time wanting to save Alice (Steve) and talking to himself in case Alice is there. Hopper is trying to find a missing child named Alice, but obviously since that's not his real name, it won't lead anywhere.
In this universe, Barbara is alive, she's kind of replacing Steve for the first two seasons.
The party initially knew Steve as Alice because that's how he introduced himself to Will, and that's how everyone knew him at first.
Steve or Alice was there first the fall in the upside down, so it was he who named the upside-down world, which is therefore called Wonderland in this AU. The Demogorgon are tweedle dee and tweedle dum, The queen of hearts=Vecna, The hatter=Mind flayer, ect, ect. The Party calls him that too because Will calls him that too because of Steve.
Then season two begins with all the mess, But it's quite different since Barb is alive.
Nancy and Barbara still go to see Murray to have the laboratory closed down, more because "it's the right thing to do" than because "Barbara is dead". Jonathan and the one who accompanies the children in the quarry and confronts the demodogs. Afterwards everyone ends up at the Byers' place, just like in the canon.
Everyone separates, and Barb and Nancy stay with the children and go to the tunnel. Where they will meet Alice, aka Steve, in the tunnels brought by his dogs. And Steve, who has remained stuck in a creepy world and who has remained more or less sane thanks to his fairy tales, will start seeing Nancy like a knight, He will often call her "My Knight" in the future. (Yes, he has a bit of a crush on her, but it's more like a child and a prince charming in a movie, or a fan and a celebrity.)
Then the gate is closed and everyone finds themselves at the hospital where Alice and Wil will be delighted to see each other again. Hopper will do some research and will eventually understand that "Alice" is actually Steve Harrington, who was reported to have died before he arrived. Since it's complicated to resurrect a child seven years later, the government will give him a new identity. Hopper will therefore find himself with two children, Steven Alice Hopper and Jane Eleanor Hopper.
Steve's outfit in Wonderland was obviously heavily inspired by Alice's.
He has slightly longer hair with a black ribbon on his head, like Alice.
He has a stained white shirt, with a black and yellow dungaree skirt like Alice's, underneath he has pants that we can't see because of the long skirt/dress and black boots that go up to the knee.
In this universe, he has a large axe to defend himself.
Mutation: All five senses are better, his heart and breathing are now slower, he's immune against poison air of Wonderland, and he's slightly stronger, and more resistant.
That's all for now! I'll probably do seasons 3 and 4, and maybe even 4.
For those wondering if there will be any Stancy, sorry but no! Steve just has a childish crush. There might be a couple, but I'm not sure.