If Unity has some fancy prebuilt shader library he's leveraging to generate the effects, reimplementing that from scratch might be a lot of work.

Scanlines and vignette are simple to implement and the main stylistic shaders they use. They also use a grayscale one if you trigger a specific situation. There might be others, but again, simple to write.

They also use the particles system for candelabras. Could be reproduced in many engines.