TMBS characters if they had Scratch:
Rhonda would tell Mr. Benedict about Scratch, and he'd like the idea and help the kids make accounts.
Reynie would be a community helper. He'd probably be in the Scratch Welcoming Committee and Scratch Design Studio. He'd create and curate a bunch of random studios and make lots of friends! He'd also have a very ✨️aesthetic✨️ profile. Anything he would code would be pretty simple but well-made, maybe point-and-click type stuff.
Sticky would definitely be an ATer (active on the advanced topics forum). I think he would be physically incapable of coding a project without using any of the trigonometry blocks. Most of his posted projects would be WIPs of engines, simulations, and 100% pen stuff. He'd try his hand at a bunch of games, which all have perfect code but dirt simple graphics because he can't art. Maybe he could try doing a collab sometime.
Kate would post mostly animations and probably a few remixes. I think she'd be great with vector art! She'd probably make zany and cartoony stuff, not generic stickman projects. Maybe she'd also post some silly spoof games, probably for the Scratch Design Studio. She would also love and favorite almost every project she sees so her profile would be a mess.
Aside from the simple default-sprite games Mr. Benedict would help her make, Constance would post only remixes. Not exact-copy remixes, but remixes intent on ruining the original project. She'd use them to parody the original, break the code, add terrible sound effects, all that jazz. She would be the type to start flame wars on other people's profiles. Once she finds the forums, she'd start trolling people, and get herself banned. And instead of telling Mr. Benedict what happened she'd keep creating new accounts but eventually get banned on those too.