It’s the main body that has to die on the Quest Bed and the dream body ascends. 

He’s with Aradia in the dream bubbles.

The Red Miles are an attack that the Black Queen’s ring grants you the ability to use. Bec Noir was able to use them to destroy Bilious Slick because he had the powers of a First Guardian.

A Sacrificial Slab is located at the center of a moon of Derse or Prospit. A Quest Bed is located some where on the player’s planet. To ascend on a Sacrificial Slab you need one body, to ascend on a Quest Bed you need both bodies.

Yes, first with Jaspers’ corpse and second with the Eldritch Princess Doll.

It’s transferred to their dream body on Skaia.

Possibly because they’re two sprites? We just don’t know. 

Yes

They were most likely able to merge because Rosesprite had only been prototyped once and could still be prototyped again. I doubt that two fully prototyped sprites could merge but hopefully spriting mechanics will be explored in more detail soon.

They would most likely revive. A Just death happens only if the godtier has turned evil or is committing evil acts.