So the format is each person makes four decks, one for each faction. You see your opponent's lineup and ban one of the four decks. Then you need to win once with each of your remaining three decks. After you win with a deck, you can't use the deck anymore.
If you know the other guy will have a Dagon deck, you can not ban that deck, and get each of your three wins against that Dagon deck. That is, for your opponent to win the match, he must win with that Dagon deck. Since he can't get that Dagon win vs. your hyper-teched lineup, you win.
Make sense?
But then why would you choose to do this against Dagon? The other decklists are pretty straightforward, too. Maybe you'll see Skellige Axemen, but NR Combo, Nilfgaard Mill, and Scoiatel Control are all basically locks. Why not just tech to beat Mill, rather than feeling obligated to allow the opponent to utilize Dagon and then try to beat Dagon three times over, when that is the strongest deck (and honestly hard for some builds to tech against).
Fair point but there are five factions. It's possible someone brings NR Skellige Monsters Elves. You could argue that based on power level alone other players are going to have a NR deck and a Skellige deck, but there are different viable Skellige decks (axemen), and while NR is almost certainly combo, it isn't that easy to tech against. I'm not even sure what I would tech against NR combo - Scorch of course, and preferably other ways to deal with big minions, but aside from that how does one tech to beat it?
Against that you're almost guaranteed to play against a monsters deck, and Lacerate is super effective against all variants. Dagon is hit worst by it, but Eredin is hit almost as hard. Cards like Archgriffin also do serious work against both decks. I feel like it could still have been done, idk.