Battle Royale evolves. The combo that is currently dominating the format is not one that I have found in any forum post or strategy article on this site. And this combo can come up in regular Dominion... for example, this kingdom:
Hamlet, Menagerie, Watchtower, Tactician, Outpost, Upgrade, Squire, Procession, Fortress, Rats (+ Colonies, + Shelters)
I can win that kingdom regularly in 7 turns on goko. The combo involved is much easier to set up than the Masquerade pin.
And here is why I like Battle Royale:
How long would it take to discover this combo playing regular Dominion?
I'm guessing decades. It takes millions of games to get the component parts together in the same kingdom, and then one of you have to be a savant who can recognize in the time it takes to make the first buy exactly how they interact together, and what's the best path to getting them your deck. And once that game's done, you can forget the combo even existed because you won't see the situation come up again for millions of kingdoms.
Battle Royale is about discovering the best synergies in the entire set of Dominion cards. My brother came across this combo because he spent an evening on his own wondering how he could exploit Upgrade to the max... and discovered that Upgrade/Fortress creates a chain to gain every single Upgrade for just 1 action (with your deck drawn). Similarly, Rats, on its own, can create a chain to gain all the Rats. Plow through one other pile and the game is over. (Moral of the story, watch out for cantrips that can gain themselves...)
I spent one night learning all the different ways to exploit Squire. (Best so far: open with Watchtower, buy a Squire with Watchtower in hand, top-deck a Margrave, who subsequently gives you cards and buys to top-deck 2 attacks on future turns... where I prefer the non-terminals Minion and Familiar... Familiar can sometimes be Graverobbered into a turn-6 top-decked Possession.)) I've also played a lot of Governor/Forge and Governor/Possession (both fun)... in addition to the standard killer decks like Native Village/Bridge (a dud) and Ironworks/Silk Road (too slow).
Right now Upgrade/Fortress is unbeatable. And when both players know that Upgrade/Fortress is unbeatable, the mirror games actually are very interesting... if you don't get 8 Upgrades, you can't pile out the Duchies in one fell swoop... and it's hard to justify any Rats in your deck if you can't auto-deplete 3 piles in one turn.
But the discussion isn't always about banning... we've actually considered un-banning King's Court or Mountebank to see if that allows for something else to compete with that combo.
Right now I know of only 4 people in the entire world that have played Battle Royale. We've played no more than 30 games in total. And yet, I think we've broken ground in Dominion strategy by identifying an unyet discussed 7-turn game-winning combo.