* The Astrolabe's imagery shows The Night King destroying the Wall, the Red Wedding, & the birth of Dany's Dragons as 3 great moments in Westeros History, in parallel (and reverse) to the original imagery of the Doom of Valeria, Robert's Rebellion, & the Rise of House Baratheon.
* The tiles that were flipping, flipped from snow to ice, signifying the distance covered by the White Walkers by the end of the episode. They've ran over Last Hearth and looks to have killed off the last of the Umbers and converted them into undead. As of the end of the episode they are at the Last River.
* The sky is much darker over the lands of the North regions (darker the further back towards the Wall), to set an ominous tone as the undead army marches for Winterfell.
* The mountain Last Hearth is on is in a spiral pattern similar to Jon's body in the hall.
* The gold dotted line that ran to the left of the icy tiles was the Kingsroad leading up to Castle Black and down south and west to Winterfell. One could expect Tormund, his freefolk, Eddison, and most of the Night's Watch to take the Kingsroad quickly down south to beat the undead Army to Winterfell and warn of impending doom. (They might not make it in time and may also be wiped out as Kingsroad intersects with the Undead Army's due course).
* The intro is much more on the ground level now that the storylines have been cut down to what's going on (and about to happen) in Winterfell, as well as King's Landing. There's likely going to be more scenes in the Crypts of Winterfell, as well as a possible escape route (for the main characters) if and when they are overwhelmed by the undead army.