I need MORE OF THE INCREDIBLES AU! omg that was so AMAZING! I'M STILL GEEKING OUT ABOUT IT!
Hahaha, I'm glad you enjoyed it! It felt so weird for me, but I'll do anything for wifey. I don't have nearly the time I'd like to continue it, but I do have some headcanons for this AU.
Hiccup becomes Tinker, as seen by the end of the drabble. He names his little batcave workshop The Forge, because he mentored under Blacksmith (Gobber). He basically spends all of his time either building fancy weaponry for the league, working on a stretchy suit that won't cut into Twist's (Astrid, obv) skin, and swatting his cat away from the computer screen while he monitors the league's tech stats during battles.
His cat, Toothless is the only animal allowed in the Tower (picture teen titans, that's basically what we've got here.) because Stoick and Hiccup basically live on site with the league. Toothless is always chewing on very sensitive Forge equipment, tearing holes in peoples' costumes, and causing general chaos, but the heroes come to accept that to get the coolest toys from Hiccup, they gotta be nice to the cat. Astrid, particularly, finds herself the victim of clawed pounces when she stretches/withdraws her arm or fingers out without paying attention.
Stoick and Hiccup's relationship is a secret, so they keep getting caught in like weirdly familial/intimate situations. They always like blush and stammer out excuses weirder than what's actually going on. Some people suspect, and some people are just jealous that the non super gets so much of The Vast's attention.
Snotlout actually doesn't make the league, to his extreme irritation. His super strength helped him sail through the qualifiers, but at a closer look, his teamwork scores were too low. Still, he doesn't take no for an answer and usually ends up showing up and working with the league anyways. Hiccup eventually makes him an unofficial league badge and later talks Stoick into letting him in.
Astrid doesn't socialize much at first. She's pretty hardened after witnessing the death of her uncle during a fight with a villain. Astrid is always in the Forge, talking to Hiccup while he works, because she likes the cool stuff he makes. They talk, and his sassy and sweet conversation style eventually gets her to open up. She's a great assistant, because no tool is too far for her to reach, and it fondly reminds her of her days side-kicking. It's her association and Hiccup's skill that gets all the heroes to respect him.
The twins can separately only control one element. Ruffnut, water. Tuffnut, fire. Their favorite skill, though, is using them together to create huge steam explosions.
Rolodexter (Fishlegs) and Hiccup have a sweet bromance. They end up sharing geek fests over Tinker inventions, and Rolodexter ends up getting tons of sweet gear because of it.