Arbitrary code execution encounter but it's temporarily a nicknamed Pokémon like Ghost (Yellow)
Notes: This is a proof of concept, and the code I made isn't optimal at all. It's a response to a question if it's possible on Twitter, and the answer is yes by calling initwildbattle part way through (see the .isGhost part), or you can just lock wEnemyMonNick with OAM DMA hijacking.
https://github.com/pret/pokered/blob/95ec2cf039f0efdc6dadfb6fe766ace231a1b6b1/engine/battle/core.asm . Note my code is extremely shoddy. You should be able to further modify it to change the front sprite. The save file should be able at https://sites.google.com/site/torchickens2/pokemon-save-files as usual.
There's also some odd memory corruption after battle.
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