Nice update. Looks a lot better than the original. The main comment I still have is one that I have for a lot of articles: your section on "deciding to Tunnel" reads more like a list of combos than an explanation based on fundamental concepts augmented by examples. The way I would have organized it is as follows (I was planning on writing a Tunnel article myself but didn't have the time):
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There are 2 main reasons to go for Tunnel: for the cheap VPs and for the reaction. The cheap VPs are nearly self-explanatory -- just get them in the late game or use it as a pile to empty in a cheap-VP rush along with Gardens or Silk road. The reaction is a little more complicated. It may not be immediately obvious, but you need 3 things to make the Tunnel reaction really work for you:
1. A way of dicarding cards -- this is the obvious one
2. A way of making sure that Tunnel is one of the cards you discard -- it doesn't help you to discard 2 cards every turn with Oracle or something if you never actually get to discard Tunnels.
3. A way of leveraging the Golds you get into something good -- this is the most subtle, but still very important. If you're buying Tunnels, your deck is going to have more Golds and VP cards than usual, and fewer Silvers and action cards. You don't have a high density of good cards, but rather a high variance in card value, and you want cards that leverage this, like sifters.
There are a few cards that give you all of these functions in one, and thus make good two-card combo strategies with Tunnel:
- Heavy sifters: Warehouse, Embassy, Storeroom. These cards give a discard from hand (1), help get Tunnel in a postition to be discarded by drawing before the discard (2), and offer sifting to help collect the Golds together while dumping the excess VP cards (3).
- Vault. [You wrote this one already. The key is that while it's a little weaker at (2) than the heavier sifters, it's much better at (3), which makes up for it.]
- Young Witch. Young Witch goes about accomplishing (3) in another way. It's not great at turning Golds into Provinces, since you need 2 Golds and 2 Coppers in 6 cards which will likely also include Tunnels and Curses, but since it drags the game out with the Curses, you can often still get to that point. Of course, if you can find a better way of accomplishing (3), like Remodel or Salvager, that can definitely help.
The example of using a late-game TfB card with Young Witch brings us to the next idea: using multiple different kingdom cards to cover all your needs. Here you get (1) and (2) from Young Witch, and add in Remodel or Salvager to provide/strengthen (3).
An illustrative example is using the Horse Traders/Tunnel "combo". At first glance, you might think that Horse Traders + Tunnel makes a good strategy. It certainly covers (1). The problem is that it's pretty bad at (2) and terrible at (3) -- you need to draw HT and TWO(!) Golds in a 5-card hand to buy a Province, which is no easy task. But clearly there's a synergy here. You can turn this into an actual strategy by adding something like Stables or Lab. By providing non-terminal draw, they help get Tunnels in a position to be discarded (2), and by increasing handsize, they make it easier to turn Golds into Provinces (3). In a six-card hand, you just need a HT, a Gold, and 2 Coppers, which is much more easy to manange. The strategy should thus be something like opening HT/Silver to hit a few early 5s to get your Stables/Labs, then start buying up Tunnels.
This is an example of the more general strategy of going for hand-size increasing + discard from hand. The discard covers (1), and the hand-size increasing covers (2) and (3). You can do this with 3-card-combos like HT+Stables+Tunnel, or you can take it more to the extreme and build a full-on deck drawing engine for the hand-size increasing, and use a discarding engine piece (Cellar, Hamlet) for discard.
Other cards provide multiple functions, but need some help to complete a strategy. Examples include Cartographer (1,3), Minion (1,2), etc...
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I'm not trying to re-write the article for you here, but the big point is that if you start with the list of things you need, you give a whole big picture to look for, than can explain how all the good (and even marginal) enablers fit in. I feel like if you incorporate this big-picture concept early on, then along with all the other content and examples you have, you'll have a really good article.