>>56713205The development docs reveal that a few gen 3 evo lines had their role in the story picked out before they were designed, one example being that it was apparently decided that Wally would have a new 3 stage Psychic type for a partner before any work was done designing Ralts' evolution line.
The scratchpad for Ralts's sprite also has what looks like an incomplete attempt to sprite the bioluminescent neuron dog thing from those spooky concept art pages, and the fact that this is the only place to find said sprite implies that it was the original candidate for the role. I gotta assume it was scrapped or redesigned into Ralts since there's no way you could realize psycho dog as a decent looking GBA sprite.