[Script] Diving sprite

Hello, I've made the HM dive work in fire red and I also made a map with underwater tiles, then the player moves in the sand (like in RSE) but I'm actually moving with the surfing sprite. That's a problem because the pokemon sprite seems to be "swimming" in the sand... and the result will be worse in the seaweed I guess.
In Gen3 versions, the sprite is above the sand, which makes more sense.

So, how could I use the diving sprite ? I know that this sprite is somewhere in the rom, but even if I knew where it is, I couldn't display it in the game. I don't even know how to change the player sprite.

another question: I've made some research about behavior bytes but I only found how to change the scripts. how can I know what bytes are used or unused in the game ? is there an exhaustive list somewhere on pokecommunity ?

edit: in gen3 versions, the sprite is the same while surfing and diving actually, I just realized... the sprite is like floating on the water and therefore it looks good no matter where he is (underwater or surface). But that doesn't help me anyway... I still need a way to change the sprite when diving.

https://www.pokecommunity.com/showthread.php?p=9612067#post9612067

For Dive to work correctly in Fire Red you should use that ASM Routine.

There is no diving sprite in a Fire Red already, as far as I know. You'll need to make/find one yourself and import it.

You can import Dive script from Emerald or Ruby.