...Fawkes?!

Aurelius/Credence is the central mysterious character in the Fantastic Beasts series, so there must surely be a reason for showing his full back story, and also weaving him into the Dumbledore family even though he is never mentioned in any of the Harry Potter stories...

...or maybe he is the driving force behind the entire saga!

The phoenix, Fawkes, is the source of the two tail feathers that form the powerful magic cores of Voldemort's and Harry Potter's wands. One is dark, one is light.

Credence Barebone had to obscure his magic power for most of his life, and unaware of his lineage, he is torn, conflicted between the light and dark.

Credence is the host entity to a powerful dark and fiery 'Obscurus', with an almost immortal quality. His dark twin.

At the end of FB1, Credence was apparently destroyed by the Aurors, his ashes filled the air and fell to the ground...yet he somehow survived?! (The boy who lived!)

And in FB2 + FB3, we now see that Credence/Aurelius has a strong affinity with a Phoenix!

In the official book 'Fantastic Beasts: The Secrets of Dumbledore: Movie Magic' it is confirmed that the phoenix seen in the FB3 movie is NOT Albus Dumbledore's phoenix, Fawkes. Yet in the numerous posters and advertising for FB3 it clearly implies a magnificent golden phoenix arriving in the Hogwarts wizarding world.

Ezra Miller wore a 'feathered bird' jacket at the FB2 premier in London. Images from the premiere show him with both arms outstretched and the Avada Kedavra curse written on the palms of his hands. An allusion to the two tail feathers / magic wand cores?!

Aurelius means 'The Golden One' in Latin.

From the novel: Harry Potter and the Chamber of Secrets (American print version):

"Fawkes" said Harry thickly. "You were fantastic, Fawkes..."

It would be a really neat way to connect the two movie sagas, with Fawkes being the core to the whole story.

And would give true meaning to the movie series title 'Fantastic Beasts'.