Um, not to be flippant, but first you say that engine is the way to go on 95% of boards, but then you say that random boards won't do and good engine boards must be constructed. What am I not understanding here?
Nah, you can't make an engine 95% of the time. I guessed BM+X is decent on about 5% of boards, but, as you pointed out yourself, there are quite a number of other possible boards/decks beyond engine and BM+X. Many cursers, including IGG, invariably turn games into slogs. Swindler by itself makes most games it appears in into retarded crapshoots. Rebuild is dominant on most boards, and it alone appears in like 5% of randomly selected kingdoms. Then there are all sorts of combo decks, like Tunnel + Warehouse/Storeroom/Vault, Fool's Gold + Storeroom/Council Room/Wharf and Bishop Golden deck. Not to mention various rush strategies like Ironworks-Gardens/Silk Roads, Vineyard rush/slog, Duke games, Trader/Masterpiece-Feodum, etc.
In addition to this, most boards contain at least one other trasher besides Butcher, which will almost always be preferable for Copper trashing, but my claim wasn't that in most Butcher games you want to be butchering Coppers:
Yes, having other means to trash your Copper is almost always better, and because other trashers are usually available, in practice you won't be using Butcher or Remodel to trash Coppers all that often. But it does not follow from this that it's a bad play.
Taking all this together should show why you can't just play some randomly selected boards to experiment with the viability of Butchering Coppers. Again this doesn't mean that you almost never want to do it:
A game from yesterday where on T9 I Butcher a Copper into an Oasis.
A game from two days ago where I remodel a Copper and a Curse into Havens, and where I'd have been remodeling Coppers more aggressively had I not been keeping them for the Mint I was going to buy the turn my opponent resigned.
This thread that was already mentioned provides a clear case where you want to Remodel (Butcher too, had it been available) your Coppers into Embargoes.
I guess I'm still at the level of skill where it seems like there are decks worth making in between BM+X and draw-your-whole-deck-for-a-megaturn. Would you say that's not valid at the highest levels of play?
Yes and no. Many boards just won't allow you to make an engine or sometimes they contain really strong non-BM+X alternatives, so in that sense you'll always be building quite a number of decks that are neither engine nor BM+X. When it specifically comes to engine-BM hybrids, however, the pure draw-your-deck-engine (not necessarily for a megaturn) is pretty much always superior. The most common mistake I see is players getting ahead in terms of deck building, but then giving the game away by spazzing out and randomly buying Golds or green cards.
This is my all-time favorite example. I get atrocious early draws, but when my opponent buys a
Curse Gold on T6 I just know that I'm going to win, even though it takes me 33 turns to get there.
EDIT: After playing a bunch more Butcher games with Copper trashing in mind, I'm beginning to come around. Butcher is still one of the worst ways to trash Copper, but it's a better idea more often than I gave it credit for.
Sounds like we're in agreement, then