It'd be a cool idea if that Pokémon ended up with different base stats and abilities and was able to learn different moves depending on which Pokémon it evolved from. It'd make that Pokémon pretty unpredictable in battles.
This would actually be a great way to play with giving a Pokemon multiple different possible move pools that are mutually exclusive. Maybe the final Pokemon can only have Spore as a result of it having been on Prevo A's level-up list or Shell Smash as a result of it having been on Prevo B's level-up list, just as a simple example. That gives the final Pokemon access to great moves but not at the same time. This can get even more interesting if Prevos have different possible egg moves or if Prevos can learn different TMs from one another that can't just be learned in their final form.
Feels like a waste really. I mean if they all become the same thing, then whats the point of the previous forms?
Something like carrying over moves / stats / types from the previous evolution "could" work in making it seem a bit less redundant, but at the same time why can't each one just have its own evolution anyway if you're going to do that? That'd be basically making each evolution unique but slapping the same appearance on it. Just make a fully unique evolution for each one.
~ Master of Electricity ~ Electro: 0518-6613-7620 - Pokemon White
I had a somewhat similar idea a while back regarding the Pan/Simi monkey trio. Basically, you'd be able to evolve each of them one more time into one of three type combinations by using an evolution stone along with some other new method (like having a high friendship through Pokemon Amie or whatever). So it would be like:
Simisage + Fire Stone = Grass/Fire type Simisear + Leaf Stone = the same Grass Fire type
And same goes for the other combinations. There's only three new Pokemon, but there's two ways of getting each.
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