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This has been on my mind for a long time:
>Since you're champion, you'll fight strong trainers one after another instead of rematching the Elite 4.
So basically after defeating the Elite 4 and becoming champion, you'd still be able to take the "Elite 4 challenge", but now since you're champion you'd fight these really strong high-leveled trainers instead. And if you lose to one of them, you then have to re-plow through the Elite 4 like the first time.
Just imagine it though, intense speeches from trainers who went through a different but equally difficult journey as you, all in the hopes of taking you, the champion, down.