I thought Legends couldn't Evolve?

Question

A sudden transformation of Carbink, its pink, glimmering body is said to be the loveliest sight in the whole world.

I thought Carbink couldn't evolve?

A transformation of Carbink into Diance is still technically evolving right?

I'm just curious to why the Pokedex says that.

Comments

Also, cosmog evolves, even though its technically a legendary.

Answer 1

That Pokedex entry is likely referring more to a Darwinian evolution, rather than a typical Pokemon evolution. The idea is that, a very very long time from now, environmental factors may cause Diancie to become more common, and eventually it may become a regular Pokemon rather than a legendary or mythic.

Comments

Darwinian evolution, the process by which species change over time.  For example, dinosaurs evolved over millions of years, expanding from a common ancestor to a very wide variety of forms.  Depending on who you ask, modern birds are, in fact, still descendants of a specific group of dinosaurs today.

Another example is the wide variety of dogs that exist today.  They are all descended from wolves, based on interactions with humans in our early societal phases.  After a while we started selectively breeding them for certain traits.  Excellent herding skills like the Australian Shepard, their ability to guard and protect like the German Shepard, and even just to be cute like the Pomeranian.

Answer 2

A similar question has been asked about the relationship between Carbink and Diancie. But, they do not evolve into each other, it is simply a theory.

Diancie is born from Carbink that undergoes a mutation. It can instantly create diamonds by compressing the carbon in the air; these diamonds can then be used to defend itself. This theory suggest that they are related to each other, but do not have an evolutionary connection in any certain way. The use of transformation is to give an idea - seeing that they are both The Jewel Pokemon.

So, just like other legendaries - but in this case, mythicals - they do not evolve.

Source
Hope I helped! :)