Oriri ex cinere was the caption alongside THE_FINALS_Concept_Fire_1920x1080.png and THE_FINALS_Concept_Firee_1920x1080.png posted here and here respectively, and later in higher resolution in the official art channel here
Image Methodology
Using the two original images as layers in photoshop and applying a difference blending mode, followed by a levels adjustment layer with the whites squashed all the way to the left (resulting in black 0, grey 1, white 2) leads to the following image:
The hidden image was determined to be of the Pisa Griffin in this post.