In a standard solitaire game of Dominion, it's the beginning of your turn. You have no cards on any mats, no Durations in play, and no active Princes. There are no Events on the board.
You have somehow reached the following state: none of the cards in your hand or deck cost more than zero, except for one King's Court and one Forge.
At the end of the same turn's Action phase, you play King's Court on Forge. Which of these sets could represent the three cards you gain as a result, and how?
Copper, Copper, Copper
Estate, Estate, Estate
Silver, Silver, Silver
Duchy, Duchy, Duchy
Gold, Gold, Gold
Province, Province, Province
All of these are pretty easy to get with lots of Highways in play? Even without Highway, my hand can simply be KC, Forge, Trusty Steed: play Trusty Steed for +2 actions +2cards, draw Moat, [whatever card I want to gain], play Moat, draw [whatever card I want to gain]x2, Play KC-Forge, trashing one card each time, and gaining the same card. Or am I misunderstanding something?
Highway costs more than $0. So do Moat and [whatever card you want to gain], unless [whatever card you want to gain] is Copper.
No cards in your deck cost more than zero, besides KC and Forge. So no Moat, nothing besides $0 cost.
Here's what you do to get more than just copper.
Play Trusty Steed in a hand of KC, Forge, Copper, Copper, copper. Choose +2 actions, +2 cards. Draw Princess and nothing else. Play Princess, KC Forge with a card draw modifier token, and you can get Estates in this way.
You can also gain Gold in this way. Draw Princess/Bag Of Gold, and you can play BoG, and choose to either play or not play Princess. Either way, you end up drawing it for each trash, getting 3 gains as a result for Gold.
You can also gain Silvers via this method. Have a hand of KC, Forge, Trusty Steed, with the same Forge Coin Token Draw. Play Steed as Gain 4 Silvers and 2 Actions, forge Silver for Silver.
You can also gain duchies theoretically, if you can get the gained Silvers in hand without running out of actions while playing Princess. Just trash 3 Silver, and don't touch the 4th one. Sadly, I cannot get to this game state so far.
Even harder is gaining Province, which requires you to get all 4 Silvers in hand AND the BoG's Gold in hand, still having to play Princess. Trash Gold and 4Silvers, and you can gain/Trash Province 3 times as well.
It's possible to gain everything, but having enough actions to do it is the challenge.
I considered Followers Draw and Ruined Village with +action tokens on them. So far nothing, but knowing DG, there has to be some elegant beautiful solution.
If you can prove Duchy, you can likely prove Province.
The problem is piss poor draw. If you can find the draw and the actions to implement it, you'll go very far. Using Followers/Ruined Village is as if you didn't even have them in hand.
Transmute could maybe get you going, if you're allowed to use it, since it's technically 0$, but I think P eliminates it from contention.
EDIT: DUH. Madman makes all gains easily possible, I don't even need to prove it.
Problem solved.