[Question] Is this even possible?

[Blank__Void]

So I'm planning out a game (using an emerald rom hack), and I came up with an idea for a battle mechanic that I'd like to implement, but have no idea if it's possible. My game features eldritch horror themes, and I wanted the antagonist team grunts to transform into Eldritch abominations at the end of their trainer battles. So basically you fight their pokemon, but when they get defeated they transform into these Eldritch abomination and you have to fight them. Theoretically it should work the same way that a regular pokemon battle would, but in this case it would have an altered swap in animation since they're not coming out of a pokeball, and they wouldn't show up as a pokemon in their pokeball display.

Before I get too attached to that idea I wanted to see if that's even possible to do.

 

[Robodoodle110]

Easy. After the trainer battle, there`s the eldritch horror as a wild battle. Make sure the eldritch horrors are uncatchable though. Pretty sure you can do that just by setting their catch rate to 0, but Master Ball surpasses that anyway.