Big things are coming up for Arya on Game of Thrones. After finally finishing up her Karate Kid training over in the House of Black and White, Arya is headed back to Westeros with a renewed purpose and a reassertion of her identity, which she'd fought so hard to shake loose before realizing she couldn't. Now that she's sure again about who she is, it's likely Arya will pick up her revenge mission right where she left off – and this time she has the skills to back up the vengeance. Arya might be seeking out old enemies in familiar terrain, and one foe in particular looks likely heading into the finale. Will Arya kill Walder Frey?
It's a really popular theory right now, which could work both for and against it. Some popular theories like Jon Snow's resurrection and Sandor Clegane's return turned out to be true, but others – Arya and the Waif's Fight Club-style split personality – never came to pass. The theory that Arya might kill Walder does have real possibility, however. There aren't a lot of clues in the show itself, but the ones there are make for a fairly compelling case. Arya might continue her old mission right where she left off.
The trailer for the Season 6 finale, "The Winds of Winter," shows some kind of banquet over at Chez Frey, and there's more than an echo of the Red Wedding to it. Over the assembled party, Jaime included, Walder intones, "The Freys and the Lannisters send their regards," which is nearly the line that preceded the bloodshed of the Red Wedding. That could be a hint that the same bloodshed is about to occur again. Even though Arya isn't pictured in the promo and fans haven't actually seen her in Westeros yet, she could be responsible for Walder's violent takedown. And if she uses the skills she gleaned from the Faceless Men, no one – Freys and fans alike – will be able to see her coming.
The first question is whether Arya would have time to get to the Twins from Braavos since her last appearance. Game of Thrones can play fast and loose with time and distance; Littlefinger seems able to teleport around the country at will, whereas Gendry is...still out there rowing somewhere? So Arya could feasibly have made the journey if the writers decide that's where they need her to be.
Earlier in the season during a training session with the Waif, Arya mentioned Walder's name once again in her kill list, so it's clear he's still on her mind. Arya hasn't forgotten the fate that befell her mother and brother and it seems certain that if granted the opportunity, that motive will push her to commit the crime. It would fit the season thematically, bringing Arya's journey full circle and taking out a major enemy in a satisfying way. And as some Reddit users pointed out, interviews with actresses Sophie Turner and Maisie Williams could hint at Arya taking out some Freys.
LauraBeyondTheWall brings up a game of Two Truths And A Lie that both Turner and Williams played for Yahoo!, wherein they both mentioned Arya's kill list. Williams said that Arya will return to Westeros, that she's in the trailer more times than people realize, and that she doesn't cross any names off her list. Turner's three statements were that Ramsay dies, Lady Stoneheart returns, and that Arya does cross off three more names. One of those claims about Arya is a lie and one is the truth, but which is which?
So close to the end of the season, they are fairly easy to deduce. Williams' first two claims were proven true, which would would make her last one a lie. As for Turner's statements, Ramsay is definitely gone, so that means either Lady Stoneheart makes a surprise return or Arya does enact some bloody vengeance. Considering Lady Stoneheart's appearance is unlikely, that points once again to Arya taking somebody out. And she'll have to work fast, because the finale is her last chance.