Let's consider the best options for this unique agenda.
At first sight, it seems two themes fit the agenda the most. There's the smuggler theme, based around giving all smugglers stealth to get those precious unopposed power bonuses. And there's the holy asshai deck that allows your opponent to witness the Power of Faith barrage. Both seem like fun, but in a tournament context, we need to look at which one is the speediest and provides the best 2-drops. Brightwater man-at-arms is basically a given, as is Oakenshield Port. The best competitive version might even drop the theme altogether and would just play the best cards.
Smugglers have River Runner and Lyseni Pirate which are both solid power-grabbers. Their naval attack icons also speed up your Oakenshield Port power production which can definitely be a factor. And the entire Seaworth family seems destined for 'nobility'. Sallador's Crew can make the casual build for immersion's sake but I'd just run Khorane Sathmantes and go from there. 3 copies of Summer Sea Corsair won't get renown, but can result in a potential total of 7 'draws' a turn, which is a colossal advantage to have turn 2. Last there's Salladhor himself, but he's not really worth playing 3 copies for. I feel some of the other characters are, given the fact the game will only last a couple of turns and you do need the card to win (and a double won't hurt).
Asshai has Intolerant Priest, Acolyte of the Flame and Fiery Followers, the latter being very expensive but quite powerful if you play extra challenge plots and R'hllor's Blessing. The priest's passive probably won't trigger but it's still decent considering the all-powerful Power of Faith. Dragonstone convert also plays nicely with the plot that you can spam twice in a row, though it's very likely Valar will find itself on the other side of the table.
Valar is perhaps the biggest problem the deck needs to deal with on a recurring basis. The only way out that I'm aware of is At the Games + Maester Lomys, or a preventive Art of Seduction to lock the opponent out for a turn, which should be enough if you design the deck with speed in mind. This does keep Power of Faith out of contention, which kinda turns me towards the Sneaky Smugglers type.
The strategy should perhaps be relative to the turn. Your setup should be about five cards, but thanks to the high number of 2-drops this will be hard to attain. Hopefully you'll get a Seat of Power and a Narrow Sea out along with two characters and a location, but that's wishful thinking.
For T1 you need those 3 extra cards. I've seen lists using King Robert's Debt or Battle at the Wall to achieve this. There's also the +2 boon and the lucky fingerbone for smugglers that can contribute to this cause. The latter can also fuel a T2/3 Mel's plot.
For T2, I guess Citadel Law is a viable option. At this stage of the game, you hope to draw into copies of Superior Claim and Make an Example. Sure, they may seem like wasted event slots, but the aggrobuild for this agenda will probably lose if you can't get past t2 based on attrition (see today's mainpage article and common logic for reference )
When the dreaded T3 arrives, you'll get a final chance to gain a quick last power with Winter Festival before a potential Valar resolves. If that fails, it's up to the mercy of the Seven I guess. No real sense holding back cards at this stage. It's practically all or nothing imo.
What would you guys play?