Combo: Donate and Delve
|Donate / Delve|
Donate is a powerful trasher; powerful enough that you might even think of taking on Debt at the beginning of the game to strip your deck down to just 3 or 4 Coppers, use those to repay the debt, and start building. For example, on a 5/2 start, you could do this turn 1, repay the rest of the debt on turn 2, take Silver on turns 3 and 4, Gold on 5 and 6... this produces high money density very quickly, but because you have so few cards, the deck will choke quickly if you just start greening immediately. Also, getting rid of the last three Copper might effectively waste another turn. Oh, and Donating uses up your +Buy.
Delve, meanwhile, is obviously a solid big-money card (and "strictly better than Silver"); in particular, it lets you open "triple Silver". But sometimes you don't want that much Silver if you're aiming for Gold, and conversely, the marginal Gold doesn't do much for a deck full of Silver - if your Copper's all gone, you need to line up two Golds for them to actually improve your chances of hitting. And if you don't have good trashing, Silver might just not be good enough for your money density. Oh, and then sometimes you use all your coins to Delve and you have another Buy from the Delve usage, but nothing you can afford....
These two Events cover each others' weaknesses in a way that produces a wickedly strong economy, very quickly. You use only Silver, never bothering with Gold. The first several turns are guaranteed - no shuffle luck is involved.
 How it works
- Turns 1 and 2: Delve, gaining a total of three Silvers; then use the remaining buy on turn 2 to Donate.
- After turn 2: Donate everything except the Silvers.
- Turn 3: Repay 6 Debt.
- Turn 4: Repay the remaining 2 Debt, then Delve. Your deck now consists of just the five Silvers, and you are debt-free.
- Turns 5 and 6: Buy Province.
Afterwards, any time you hityou can buy another Province; otherwise just Delve again, effectively doubling the Silvers you drew. This keeps your deck flooded and your money density high. This is as big-money as it gets - you don't need any Action cards!
Anything that loves Silver, obviously, such as Feodum. In this case, you probably want to buy a Feodum every turn and Delve with any excess coin, instead of taking Provinces - because you can end up with a LOT of Silver this way.
Almost any solid BM+X card should be good here as well; the humble Smithy looks particularly good since it's an even-cost card. But maybe just keeping up the Silver flood is better....
 Additional considerations
While a single Gold in a deck full of Silver doesn't help you hit, a single Platinum does help you hit - and in fact is necessary without any draw. So in a Colony game, you'd want to buy a Platinum on turn 5, and maybe add one or two more later.
Trader could be used to get Silver as well, but it's unclear if that's actually any better than just Delving more.