I have a theory that dreepy were actually tatsugiri in their last life, and i have sufficient evidence. first off, its Gen 9 dex entry states that it bites clauncher while it doesnt eat them, maybe hinting that it ate them in a past life and that its around water. in violet, it does also spawn around water too. it's evolutions also revolve around the whole 'using pre-evolution in battle'. pre-evolution could also be weaker pokemon, like dondozo uses tatsugiri. they are both dragon-type too. maybe the fact that it is a ghost gave it an ability to evolve into a very different pokemon to what its living form was.
What do you think? theres not enough evidence i have to fill the gaps but most of it adds up, right? or it could be a complete coincidence. but what do you think dreepy could've been?