Stockpile/GambleThis is a combo, that, unlike other combos, you will trigger only once in a game. And only one player can pull it off.
So the keys here are: First that Gambling a Stockpile will net you $1 and a buy. And second, when you play a Stockpile it will not stay in the game, but go to your Exile Mat, from where you can get it back to your deck by gaining another copy of it and thus potentially using it multiple times during one turn.
So how does it work?You first need to do some setup. You need to have drawn your entire deck, have at best 2 or 3 Stockpiles in Exile and have at least $5 and 2 buys. So say you got there and there are still like 5 Stockpiles in the Supply. Now you do the following:
You buy a Stockpile and discard your Stockpiles from Exile (say there were 2 of them). Now you have $2 money left and 3 Stockpiles in your discard pile. Then you buy Gamble and it will let you play a Stockpile, since there is nothing else left in your deck. This will leave you with $1 and 1 buy more then before buying the Gamble. You do this 2 more times and end up with $5 and 4 buys. Now you can buy another Stockpile and exile 3, to have 4 in your discard. If you start over again Gambling all of these, you will have $6 and 8 buys. If you keep repeating this until there is no Stockpile left in the Supply, you will have $15 and 26 buys (I hope, I got those numbers right).
This gives you a really good advantage in tempo, as you can put a lot of good stuff into your deck. Also, there might be the possibility of a 3-pile here, since Stockpiles are empty and you are already some turns into the game.
However you can even improve this by leaving Stockpiles after you bought the last one. For example one could Gamble once to ensure, the Stockpiles are on top of the deck. This will give you $9 this turn and on the next one 5 Stockpiles, in other words $15 and 5 buys, and even another one in the turn after that. Note that any extra money you had on top of the $5 you needed, will also be on top of what you end up with. If you were about equal with your opponent before that turn, you should have a big lead now and this should almost always guarantee you a win.
With Cost Reduction:This combo will get an incredible boost with cost reduction (Bridge, Highway, Inventor, Canal). Even reducing the costs of cards by one (note that this will not affect the cost of Gamble) will almost certainly give you a win, the turn you pull off this combo. First, it makes Stockpiles cheaper, which in the above example, will give you an extra $5. But more important, it reduces the cost of the cards you are going to buy in the end. If points are about equal, which will be most likely at that point of the game, you can buy 8 Estates, 10 Curses and 1 Province, which will cost you $15. This will net you 4 VP and end the game, as Stockpiles, Estates and Curses are empty. In most cases you also be able to buy an additional Duchy. And often enough you won‘t need to touch Curses, because there is like a former $2 card, that costs $1 now, that you can empty or any other pile that has few cards left.
With Donate:It is no suprise that this combo works well with Donate, but it so fast, that I want to mention it here. Take the following scenario, which is quite likely:
You open 3/4 and buy two Stockpiles. Your opponent does the same. Then turn 3 you have
at least 3 Coppers and at most 1 Estate in hand, i.e. 1 Stockpile, 3 Coppers and 1 Estate. You buy Donate, trash everything but 1 Stockpile and 4 Coppers, and have 2 debt left over. Your opponent also trashes with Donate, which of course includes trashing the Estates. Now you can win turn 4! You will have 1 Stockpile and 4 Coppers in hand, which give you $7 and 2 buys. You pay the 2 debt and have $5 and 2 buys, to work with. And that is exactly what you need for Gamble/Stockpile. There are 6 Stockpiles left in the Supply and, when you are done with all of them, you have $21 and more than 30 buys (hopefully I did the maths right). This gives you the opportunity to buy 8 Estates, 10 Curses and 1 Duchy, ending the game on turn 4 with 1VP, while your opponent has 0VP.
This of course is only an example, to underline the potential of Gamble/Stockpile.
Counters:Of course the easiest way to counter it is by buying enough Stockpiles, to take away its potential. Since each additional Stockpile makes the combo a lot better and it is quite weak with too few Stockpiles. This alone should be enough, to make it weak enough in most games, where both players know about.
Then also hurting your opponents ability to draw his deck is also a way to prevent your opponent to execute a Gamble/Stockpile turn. So junking attacks counter it. And also discard attacks will make it harder, while not impossible.
Unfortunatly, even if your opponent does not know about Gamble/Stockpile, he will likely use any of these counters anyway, because they are good on their own. So when Gamble and Stockpile are in the kingdom, the chances that you can pull it off is small. But nevertheless, watch out for it, as it can win the game for you (or your opponent).
This is my first article, so I am grateful for any feedback.