Interesting mechanics and techniques thread.
Clones, body swaps, fusions, but I'll do you TWO better:

To avoid secondary characters and one-shot characters stealing away character development and focus from main characters we are simply going to make the main character have alter egos where he assumes the closest role of his appropriate archetype. Just like MCs doing 100 jobs we let them have 100 traits. This way when the happy go lucky character goes depressed he has a bunch of personality traits added to his portfolio. Or when the annoying one turns into the charming one and vice versa.

To avoid and contrast shitty friends vs good friends we are going to give the main character 2 teams. A) the A-team B) the Ed edd eddy team
1 team that's the definitive superior quality team he's 90% satisfied with and the 2nd team that he's 40% satisfied with and always trashes them if the 2nd team dares to raise an eyebrow against him.
This way we avoid the untouchable secondary chars like Lizzie Devine and those gays hypocritical friendship lessons. We allow the MC to beat them up and trash them as hard as he wants. We also throw a bunch more lessons about picking your allies, friends, family members. Shows have too much status quo and liberal ideas, we need to learn to cut ties/burn bridges.

Clones, body swaps, fusions are only ever used for 1 episode and done terribly. We need a show that uses them 24/7.