Let’s try one of those “reblog with” things I’ve seen on other blogs.

bland-pokemon-headcanons:

Reblog with your idea for a new Pokémon. I’ll start.

I would like a dark/water type based on a leopard seal. It uses it’s strange, beautiful song to attract prey close.

More of a whole new line. 

Three seemingly unremarkable, unrelated Pokemon, at least one of which is probably based off of a saltwater angelfish. Probably one is grass, one is water, one is fire, and they vaguely look as if they could be starters, but are otherwise unremarkable.

Until they evolve. Because there are three evolved versions, and each of the unevolved Pokemon can evolve into each of the evolved versions. They may completely change type to allow for this, and the evolution is most likely either random or based on a value that the player can’t change. None of the final versions are significantly more or less common than the others, there’s about a 1/3 chance of getting any given evolved ‘mon from any given unevolved one. Also, breeding them might result in any of the three unevolved ones. 

To make this not an evil thing to do, they’re not terribly rare. Found in different areas, though, at slightly different starting levels, so it’s a surprise when they turn out to be related.