[Graphics] Rival Sprites

I'm a newbie and I am making a hack for Fire red. On nameless sprite editor, there are 3 sprites for your Rival. When are each of these used? Also, side note how do I edit my trainers in battle sprite?

If i'm correct, there's the big Intro sprite, the OverWorld Intro sprite, the normal OverWorld sprite and the battle sprites;

The big one is the one that appears when choosing the name for him, the OW intro is the one when customizing his name, the normal OW is when you see him in-game normally and the battle sprite is when you start the battle (duh), if you want all of them customized, you'll have to change all of them.

Now, your trainer battle sprite is on the "Navigation" tab, on the first folder, at the "Backsprite" option there should be another folder named "Boy" where you can find all the sprites.

I think that's all, if you need anything else, just come and ask me, if i now, i'll gladly answer :)

There's also the fact your rival changes battle sprites a couple times throughout the story, if that's what you meant by three sprites

You can find which trainer battles they're linked to specifically in a trainer editor, but descriptively here's a Bulbapedia link to his teams, the battle location, and the battle sprites for each