What is the most interesting "Wildcard" in each Plotline in TWoW?

Background

One of the things I love about ASOIAF is how a plotline can be going completely as you would expect it to go and then something happens (a side character does something or a character's objective changes, magic is introduced, etc) In this post I thought it would be fun to discuss the most interesting "wildcard" in each of the 13 major plot locations in TWoW.

Note: I am going to use the 13 locations (just because it is easiest for discussion purposes) where our POVs are scattered.

If interested: Death of a POV: There is always another POV Character Around

Beyond the Wall (POV = Bran)

There are a few options here ranging from Varamyr living on his second life in Bran's pack, to Bran breaking the "skinchanger's code", but I think the biggest wildcard comes from Bran's new abilities.

"He heard a whisper on the wind, a rustling amongst the leaves. You cannot speak to him, try as you might. I know. I have my own ghosts, Bran. A brother that I loved, a brother that I hated, a woman I desired. Through the trees, I see them still, but no word of mine has ever reached them. The past remains the past. We can learn from it, but we cannot change it." -ADWD, Bran III

If interested: Accessible Weirwood/Heart Trees & On the recent "Time Travel" Discussion

Castle Black (Melisandre, Jon Snow*)

A few good options ranging from Wun Wun to Shireen, to Patchface. But since Stannis will be involved in Shireen's death, I think a more immediate wildcard is Monster.

Burning dead children had ceased to trouble Jon Snow; live ones were another matter. Two kings to wake the dragon. The father first and then the son, so both die kings. The words had been murmured by one of the queen's men as Maester Aemon had cleaned his wounds. Jon had tried to dismiss them as his fever talking. Aemon had demurred. "There is power in a king's blood," the old maester had warned, "and better men than Stannis have done worse things than this." The king can be harsh and unforgiving, aye, but a babe still on the breast? Only a monster would give a living child to the flames. -ADWD, Jon I

If interested: Does Mel Burn Monster?

The Crofter's Village (Theon, Asha)

I think similar to other plotlines below, this hinges on the magic that will likely take place. Stannis is going to "give Theon to the Tree":

“Take him out across the lake to the islet where the weirwood grows, and strike his head off with that sorcerous sword you bear. That is how Eddard Stark would have done it. Theon slew Lord Eddard’s sons. Give him to Lord Eddard’s gods. The old gods of the north. Give him to the tree.”

And suddenly there came a wild thumping, as the maester’s ravens hopped and flapped inside their cages, their black feathers flying as they beat against the bars with loud and raucous caws. “The tree,” one squawked, “the tree, the tree,” whilst the second screamed only, “Theon, Theon, Theon.” -TWOW, Theon I

If interested: Names Said by Ravens in the Series

Skagos (Davos)

This one is tough since we only know of a few named characters (Osha, Rickon, Shaggy) besides the POV. I've read theories ranging from Rickon being worshipped as some type of warg god, to Davos getting captured (again), even to the island having the body of the Cannibal on it. That said I am going to say Osha. Strictly because GRRM has stated that he could be influenced by Natalie Tena's performance:

Interviewer: Can you think of instances in seeing these portrayals, the actor’s take that gave you a new perspective?
GRRM: When Osha comes back in the books, it’s possible, I haven’t actually gotten to it yet that she will be influenced by what I’ve seen, that I will write a more interesting character. SSM, Deeper than Swords: 26 Mar 2014 (its around the 56 min mark)

If interested: Osha's Decision: Taking the Raging Wolf to the Isle of Cannibals

The Vale (Sansa)

At the Tourney of the Brotherhood of the Winged Knights, I think our biggest wildcard is easily the Mad Mouse imo. Not only has he already met Brienne, and knows Sansa is missing, but he seems to know her identity, and that she is valuable:

"Will you be seeking wings?" the Royce girl said.

"A mouse with wings would be a silly sight."

"Perhaps you will try the melee instead?" Alayne suggested. The melee was an afterthought, a sop for all the brothers, uncles, fathers, and friends who had accompanied the competitors to the Gates of the Moon to see them win their silver wings, but there would be prizes for the champions, and a chance to win ransoms.

"A good melee is all a hedge knight can hope for, unless he stumbles on a bag of dragons. And that's not likely, is it?"

"I suppose not. But now you must excuse us, ser, we need to find my lord father. " -TWOW, Alane I

It should be noted that in an early outline of AFFC, GRRM had the Mad Mouse dying in whatever he tried to do.

If interested: Ser Shadrich of the Shady Glen aka The Mad Mouse

The Riverlands (Brienne, Jaime)

The plotline I am looking forward to the most. There are plenty of good wildcards that could happen here ranging from the missing Ned Dayne showing back up, to the brotherhood resuming their quest for Arya. But I think the biggest wildcard that could take place is if GRRM chose instead to use the magical ending he originally had for Brienne in the Russian AFFC draft:

“Enough, Harwin. Do we mean to hang the ugly bitch or talk her to death?” The one-eyed man snatched the end of the rope from the other outlaw and gave a yank. The rope dug into skin, lifting Brienne upward. If this is another dream, it is time for me to awaken. If this is real, it is time for me to die. From somewhere afar she heard the clapping of wings. The carrion crows are coming to feast at her corpse. About a dozen already are circling over her head, but for carrion crows these birds are too large. Ravens**, smiled Brienne.** How odd**. No, it** is a dream, and now she will awake.

If interested: Brienne's Fever Dream & Lady Stoneheart: The Culmination of Numerous Riverland Plotlines

King's Landing (Cersei)

Another location with a few great options (Arriving Sand Snakes, wildfire (this is huge but also likely happens a bit later imo), etc), I think the biggest wildcard is still Qyburn.

Qyburn, thought Cersei. That was good, one straw at least that she could clutch. Lord Qyburn had them, and Lord Qyburn could do wonders. And horrors. He can do horrors as well. -ADWD, Cersei I

If interested: The Bloody Maester: Discussing Frankenstein & not just his Monster

Storm's End (Jon Connington, Arianne)

I will go with Elia Sand here. One of the Sand Snakes, she is part of Arianne's party that travels to the Stormlands. GRRM has seemingly been building up her "wildness":

And Elia Sand, oldest of the four girls that Prince Oberyn had fathered on Ellaria, would cross the Sea of Dorne with Arianne. "As a lady, not a lance," her mother said firmly, but like all the Sand Snakes, Elia had her own mind. -TWOW, Arianne I

If interested: What is Lady Lance going to ruin in TWOW?

Oldtown/Off the coast of SW Westeros (Sam, Aeron)

We have whatever Leyton has been up to for the last decade, and super important Sphinx and a horn possessed by Sam, but it has to be whatever Euron is summoning. Euron's potential hinges a lot on it imo. Krakens are cool (and likely), but you are not bringing on the apocalypse with them:

If interested: Euron Greyjoy: The Summoning

Dorne (Areo Hotah)

Our Camera that Rides is traveling with Obara Sand and Balon Swann to take down Darkstar at High Hermitage. One wildcard would be Ned Dayne showing up (since no one in Dorne misses him anyway) but I think the biggest wildcard would be the often discussed Darkstar stealing Dawn theory.

If interested: Gerold "Darkstar" Dayne & A Thought on Dawn

Braavos (Arya)

I think the death of Raff the Sweetling:

“You’ll need to carry me.”

See? thought Mercy. You know your line, and so do I.

“Think so?” asked Arya, sweetly. -TWOW, Mercy I

is going to cause major problems in Braavos:

This would make trouble for the Sealord and the envoy with the chicken on his chest, she did not doubt.

If interested: Let's talk about Braavos in The Winds of Winter

Slaver's Bay (Victarion, Tyrion, Barristan)

We have a few great smaller options, the Windblown and the Second Sons switching sides back to Dany, but due to proximity and immediate impact, I think it has to be the dragonhorn. I can't claim to know who it will work for exactly:

'Blood for fire, fire for blood.' Who blows the hellhorn matters not. The dragons will come to the horn's master. You must claim the horn. With blood." -ADWD, Victarion I

but something is going to happen with it being blown and Rhaegal right there:

By the time Plumm and his companions came galloping back from the camp of the Girl General, the white dragon had flown back to its lair above Meereen. The green still prowled, soaring in wide circles above the city and the bay on great green wings.

If interested: Dragonbinder: Claiming the Horn

The Dothraki Sea (Daenerys)

While I do think Dany is supposed to go see the Dosh Khaleen/become the "Stallion that mounts the World":

Beneath the Mother of Mountains, a line of naked crones crept from a great lake and knelt shivering before her, their grey heads bowed. -ACOK, Daenerys IV

I think the biggest wildcard is Drogon himself. Does he let the Dothraki take her? Or do they bow to her right there after some display of strength, etc:

As the western sky turned the color of a blood bruise, she heard the sound of approaching horses. Dany rose, wiped her hands on her ragged undertunic, and went to stand beside her dragon.
That was how Khal Jhaqo found her, when half a hundred mounted warriors emerged from the drifting smoke. -ADWD, Daenerys X

If interested: To Go Forward You Must Go Back

Bonus: Prologue in the Riverlands/Westerlands (Unknown - Jeyne Westerling "Appears")

With Jeyne's hips being debunked, the biggest things that usually pop up here are Ilyn Payne (also debunked) or some type of attack by the Blackfish, Brotherhood or Nymeria's wolfpack (or some combination of them all). I do think Nymeria's wolfpack killing them indiscriminately would be quite wild.. (I will also note that Nymeria wolfpack doesn't seem to be in the direction they are heading but that doesn't matter too much).

Except in dreams. She took a breath to quiet the howling in her heart, trying to remember more of what she'd dreamt, but most of it had gone already. There had been blood in it, though, and a full moon overhead, and a tree that watched her as she ran. -TWOW, Mercy I

If interested: Whitesmile Wat: TWOW, Prologue

TLDR: Just a list of some of my favorite "wildcards" that exist across the ~13 locations in TWoW. I think that there are plenty of others I didn't mention, but my subjective list tried to combine immediate impact, size , etc. Let me know some others I may have missed or if you agree.