The parallels between the weddings of Rhaegar and Lyanna and Robb and Talisa are more appropriate than the simple, logical explanation of them both being sudden elopements under the same religion so of course they'd be similar; beyond that, they both ultimately had similar results. Robb marrying Talisa for love and breaking his marriage agreement to the Freys lead to both of them being brutally murdered and Robb's house almost being destroyed. Rhaegar marrying Lyanna dragged the realm into a bloody civil war that ended in his death and the near destruction of his house, along with the deaths of Lyanna's brother and father; even had Rhaegar managed to win against Robert, his setting aside of Elia would have almost certainly caused war with Dorne as well.
Royce being the only lord present to Baelish's trial is so he can report Littlefinger died for murdering Lysa and so Sansa doesn't lose the Vale's support. Robin won't pull his army back for the man who killed his mother. Also, while the trial has some traits of Kangaroo Court since the accusations are presented without solid proof, even though they are all true, we only have the accuser's word on it. Except Baelish let it slip that he did indeed kill Lysa, something which the Lords of the Vale questioned him about way back in Season 4. He wasn't well-liked to begin with, but after that admittance, they have no reason to defend him or doubt Sansa's word.
There appears to be no need for solid evidence in Westerosi trials anyhow. All that seems to be needed is the judge/ruler's opinion to be swayed. This is why Tyrion demanded trial by combat in Season 4.
When the argument between Cersei and Jaime concludes with him leaving, a remix of "light of the seven" plays in the background. Now she has really burned down everything.
It's even eerier considering that the Lannister leitmotif has always been "The Rains of Castamere". For all her talk about Jaime and her children and a new Lannister dynasty, Cersei's on nobody's side but her own.
Viserion now being undead:
His having tattered wings, as he crash-landed on a frozen lake filled with icicles upon being fatally struck by the Night King's spear. Also, his corpse was literally dragged over the aforementioned lake before his pseudo-resurrection.
Him being able to use fire for seemingly a far longer (if not unlimited) time since he no longer needs to catch his breath in between uses (or possibly even to breathe in general).
Euron's abrasiveness during the parlay makes even more sense when it's revealed he was waiting for a reason to be kicked out. Given how much of an asshole he is, it wouldn't even seem out of character and being told to go fuck on the rocks at Pyke for ruining the negotiation by Cersei or Jaime would accomplish the same fake desertion.
While it's somewhat hard to pinpoint what the earliest possible moment that Sansa could have caught on to the fact that Littlefinger was pitting her and Arya against each other was, Petyr's scheme could not have gone unnoticed past one particular moment: when he tried to lead Sansa into the assumption that Arya wants to be Lady of Winterfell. He doesn't know that nobility, titles, and positions of power are things that Arya couldn't care less about — but Sansadoes. If she had any doubts about his involvement before the scene, none would have been left afterwards. Her having been his Bastard Understudy also likely helped her figure out what tricks he was trying to use.
Also, he was suggesting that Arya, to achieve her supposed goal of becoming the Lady of Winterfell, was using a circuitous plan involving making her lose the support of the lords, then executing her and taking her place as her heir. The episode before had Arya mention to Sansa that if she wanted to become Lady of Winterfell, all she would have to do is kill Sansa and take her face. So, she knows that that isn't her goal, and therefore Littlefinger's ideas would then come into question.
The Dragonpit being the site of the meeting is almost certainly Cersei trying to needle and insult Dany.
When talking with Bran, Sam claims he read evidence of Rhaegar and Lyanna's marriage, and Jon's true parentage, when in truth it was Gilly. While it might be an error or Sam trying take the credit, it's more likely that, as Sam was frustrated at the time that Gilly read it out, due to having hit Rage Breaking Point with the maesters, he didn't consciously acknowledge the information but did store it, and then remembered it when Bran brought his own knowledge up later, but failed to recall how he learnt it, simply presuming that he translated it himself, it is not unusual for people to have knowledge with no recollection of where they picked it up.
Given how much he thoroughly believed he was the rightful king of the Seven Kingdoms, Viserys probably invoked the Strong Family Resemblance trope by styling his hair to look exactly like that of his big brother (and original first-in-the-line) Rhaegar.
How did Bran know of events like Littlefinger betraying Ned and lying to Catelyn about the dagger, given that they happened in the middle of King's Landing? When Littlefinger handed Bran the dagger, it might have been like psychometry with Bran using his seer's ability to read the history of the dagger itself.
Bran can see anything he chooses to see; he doesn't need a physical item to trigger his powers. He could see what happened 6 years ago in King's Landing simply because he chose to see what happened 6 years ago in King's Landing. Just like he chose to see the circumstances of Jon's birth, and he chose to see Littlefinger telling Varys "Chaos is a ladder". It has nothing to do with psychometry.
Unlike in the books, Bran's greensight doesn't appear to be limited to events that happened within range of a heart tree. And for all we know, he might eventually overcome that limitation in the books, too.
More Fridge Tear Jerker again but one really has to feel for Robert knowing that he went to war all for the sake of the woman he loved — or at least loved the idea of — without realizing that she didn't feel the same. Even if things had been different and the Rebellion had never happened, Robert was doomed to die unloved and miserable.
Not so much horror, but one also has to feel a great deal of sympathy for Elia Martell, who from all reports was a wonderful human being. When added to the circumstances of her death (and that of her children), Rhaegar setting her aside (and Lyanna rolling with it) comes across as remarkably callous and unsympathetic. Barring some ameliorating revelation about it in Season 8, Rhaegar and Lyanna's marriage (however loving it may have otherwise been) will find it difficult to avoid the taint of this.
And adding further insult to injury, after having annulled his marriage to Elia and possibly thereby made their children illegitimate, he names his son by Lyanna Aegon — the same name as his son by Elia. So Elia's son lost his legitimacy, his place as second in line to the throne, and his name to his new half-brother.
Now that Viserion is an ice dragon, is any other place outside Westeros safe? The dead may not cross the sea easily, but that can't stop the Night King from establishing a foothold on Essos, as he can fly to the Free Cities, massacre some settlements and raise another undead force from the victims (and some additional White Walkers from captured babies). Even if they establish a foothold in just one city, they can easily steam roll Essos, especially since massive military forces like the Dothraki and Unsullied are not at Essos right now. Whatever military force a Free City can muster (even a professional mercenary one) can be wiped out by the dragon. The only effective tool against the Walkers is Valyrian steel, which is not only as rare in Essos as Westeros (except, maybe, Qohor), but can only be wielded as daggers or swords, not javelins or bolts — so good luck with anyone trying to engage in a sword fight with a flying Night King on a dragon. Plus, the Free Cities are either ignorant or indifferent to the White Walker threat, such that they haven't mass produced either ballistae-with-bolts (multiple numbers of these things would be needed for mortal men to take down that dragon) or dragonglass-based weaponry (which can also only be imported from far off Asshai and, therefore, not readily available, immediately, for the Free Cities), which makes them weaker than the Seven Kingdoms and hence, easier to conquer for the Walkers. So, the idea that one can simply sail away from Westeros and just avoid the White Walkers and the Undead altogether is simply not that tenable, and Essos may also be just as vulnerable as Westeros.
Apart from that, now that the Walkers have Eastwatch, what's there to say that some of them won't commandeer a ship or fleet from its harbour, with a zombie crew, and sail to some place across the Narrow Sea — say Ibben or Braavos — and establish a foothold on Essos over there via a sneak attack or amphibious assault (with the assistance of the dragon, of course)?
There is no evidence of White Walkers ever sailing or using ships before, or else they would have attacked Hardhome to get ships and crossed into Westeros and/or beyond.
There is no reason for them to do it now but once all of Westeros is dead, what really stops them from learning how to sail? The chains they used to drag Viserion seem like those used in a harbor, after all.
Though this fridge horror is slightly softened thanks to Westerosi views on incest being much looser than a modern idea of it. From the books Tywin and his wife were cousins, as were Eddard's parents Rickard and Lyarra. And there have been uncle-niece marriages on the Stark family tree.
Without Viserion to destroy the Wall, the White Walkers would probably have to wait for the Bay of Seals to freeze completely just so they could reach Westeros without crossing the Wall. It would have been a slower path and several wights would have been lost by crossing into the thin ice. But thanks to the wight hunt, the Night King has access to a dragon and he used it to bypass the problem effortlessly.