Rival Battle

That's a fun idea, but just a bit of friendly advice: from a "trainer's" standpoint it makes sense to wait until you're ready to start the battle to actually start the battle, but from a user interface standpoint you generally want your game's players to have to click or tap or press a key as few times as possible to achieve a desired effect. I know one little extra click doesn't seem like much (and you're welcome to disregard this if you like since it is your team's game, of course), but interface design professionals tend to agree that people would rather avoid something like this if it means they get to their goal faster (in this case, being able to choose attacks and the rest of the battle interface). When it comes to making a game like this, sometimes you need to consider whether convenience is more important than realism, and vice versa. There's nothing wrong with just assuming that, yes, the trainer does want to battle by default—that's why the player picked up a pokémon battling game, after all!

If you're really attached to the idea, is there a way you could make it optional? It's cute, but when it comes down to it I personally would rather not have to make unnecessary clicks and be able to skip that extra step; making it an option would still leave it available for the people who do like it, though.

Alternatively, this would be a good place to give the player a chance to "run away" from the trainer battle or something (perhaps their one and only chance, and the option would fail as normal once the battle actually started). If your reasoning is that you "may not want to battle", then why not take it as an opportunity to turn down the battle you supposedly don't want? I'd still suggest making this optional, as again, much of the reason the player picked up the game was to battle in the first place, but at least that way there's a more concrete advantage if the player decides to take this extra step. I can think of a few times I accidentally blundered into a trainer's sight and wished I'd been able to backtrack and prepare a little better, at least.

Apologies for the lengthy comment. The interface itself looks very polished, and the background is nice and colorful. (A slightly larger font for the buttons might be nice, though, if you can swing it.) But speaking as someone who had to sit through several classes on interface design, I just thought it wouldn't hurt to offer that little suggestion in case you find it helpful.