>BackstoryYour rival is your childhood friend, who starts out all nice and considerate, like modern rivals do.
>PersonalityLike I said, he starts out pretty nice and considerate, but he begins to change after suffering loss after loss against you. It's subtle at first, with some lighthearted jabs, but then turns to full blown resentment and jealousy. As you progress in the game, you find out from other characters that his journey hasn't been going well. He gets lost, loses his first couple of gym attempts, and one of his Pokemon runs away from him, which is reflected by his team changing
>Partner Pokemon/AceObviously the starter with a type advantage, and I was thinking he starts out with a Togepi and it becomes a Togetic, but runs away. The next time you battle him, he's got a Vullaby
>TeamIt starts out with his starter and Pokemon you find naturally travelling throught the region, but as time goes on, he starts switching them out for Pokemon with known violent temperments, like Primape and the like
>What they doAt some point, your rival joins the villain team, and he's assigned a mission to do [insert bad thing here], and you're the only trainer who can stop them. He goes on about how he was never able to beat you, and how he was stuck walking in your shadow, but now he's obtained true power and it's a intense battle perhaps at some place you both have a fond memory of
>Overworld themehttps://youtu.be/zgmQ8Mp-vjo>Battle themehttps://youtu.be/nuHLz1tA0UgAfter you beat him, he realizes he's being a bitch and that while you two walked different paths, he didn't have to go down the road he did. He reforms, his Togetic returns, and he can be rebattled in your hometown and depending on if it's day or night will decide if he uses his edgy team or his more casual team.