Here's the solution to the hard mode, with 1036 points by the end of Turn 5:
Kingdom: Black Market (Bm), Chancellor (Ch), Watchtower (Wt), Bridge (Br), Ironworks (Ir), Throne Room (Tr), Council Room (Cr), Haggler (Hg), Upgrade (Up), Goons (Gn), King's Court (Kc)
Black Market deck contains: Forge, Fairgrounds, Grand Market, Bazaar, City, Contraband, Counting House, Duke, Festival, Inn, Market, Tribute, Feodum, Gardens, Silk Road, Worker's Village, Cellar, Crossroads, Hamlet, Pawn, Squire, Vineyard, Young Witch (Chancellor is the Bane) and Cultist.
Open Ironworks/Chancellor
Turn 3: Draw IrChCCC
Play Ir1, gain Tr1
Play Ch1, discard deck
Play 3C
Buy Wt1
Turn 4: Draw TrIrChWtC
Play Tr1-Ir1, gain Ir2,Tr2, reveal Wt1, top-deck both
Play Wt1, draw Ir2,Tr2,2C
Play Ir2, gain Br1
Play Tr2-Ch1, discard deck
Play 3C
Buy Kc1
Turn 5: Draw TrKcBrIrWt
Play Tr1-Kc1:
- Play Br1 thrice
- Play Ir1 thrice, gain Kc2,Kc3,Cr1, reveal Wt1, top-deck all
Play Wt1, draw Kc2,Kc3,Cr1,Tr2,Ir2,Ch1
Play Tr2-Kc2:
- Play Ir2 thrice, gain Kc4,Up1,Up2
- Play Kc3 thrice:
- Play Cr1 thrice, draw 7C,3E,Kc4,Up1
- Play Up1 thrice, 3E-->Tr3,Ir3,Ir4, draw Up2,Tr3,Ir3
- Play Kc4 thrice:
- Play Ir3 thrice, gain Kc5,Kc6,Cr2
- Play Up2 thrice, 3C-->Ir5,Ir6,Ir7, draw Ir4,Kc5,Cr2
- Play Kc5 thrice:
- Play Ir4 thrice, gain Kc7,Cr3,Up3
- Play Tr3 thrice:
- Play Cr2 twice, draw Kc6,Kc7,Ir5,Ir6,Ir7,Cr3,Up3
- Play Up3 twice, 2C-->Ir8,Ir9, draw Ir8
- Play Ir5 twice, gain Up4,Cr4
- Play Kc6 thrice:
- Play Ir6 thrice, gain Kc8,Kc9,Kc10
- Play Ir7 thrice, gain Hg1-3
- Play Kc7 thrice:
- Play Ir8 thrice, gain Hg4-6
- Play Cr3 thrice, draw Up4,Cr4,Kc8,Kc9,Kc10,Ir9,Hg1-6
- Play Kc8 thrice:
- Play Up4 thrice, ChCC-->Ir10,Tr4,Tr5, draw Ir10,Tr4
- Play Ir9 thrice, gain Hg7-9
- Play Ir10 thrice, gain Hg10,Cr5,Bm1
Play Tr4-Cr4, draw Tr5,Hg7-10,Cr5,Bm1
Play Hg1-10
At this point, we have 27 Actions and 14 Buys, and each time we buy a card (including by Black Market), we gain 10 cheaper cards. So:
Play Tr5-Bm1, buy Forge and Grand Market, gain 20 cards (Gn1-10,Cr6-10,Tr6,Bm2-5)
Play Cr5, draw Gn1-3,Cr6
Play Cr6, draw Gn4-6,Cr7
Play Cr7, draw Gn7-9,Cr8
Play Cr8, draw Gn10,Cr9,Cr10,Tr6
Play Cr9, draw Bm2-5
Play Gn1-10
Now we have 11 Actions and 29 Buys, and get 10 VP every time we buy a card.
Play Tr6-Kc9:
- Play Bm2 thrice, buy Bazaar, City and Counting House, gain 30 cards (Bm6-10, Wt2-3, Br2-8, Tr7-10, 3 Coppers, a Potion and 8 Ruined Markets)
- Play Kc10 thrice:
- Play Bm3 thrice, buy Festival, Market and Tribute, gain 30 cards (30 Coppers)
- Play Bm4 thrice, buy Worker's Village, Cellar and Inn (shuffle Cellar and Counting House into deck), gain 20 cards (20 Coppers)
- Play Bm5 thrice, buy Crossroads, Hamlet and Pawn, gain nothing
Play Cr10, draw Counting House, Cellar, Grand Market and Forge
Play Counting House, draw 53 Coppers
Play Cellar, discard 37 Coppers, draw 37 cards (Bazaar, City, Festival, Market, Tribute, Worker's Village, Inn, Crossroads, Hamlet, Pawn, Bm6-10, Wt2-3,
Br2-8, Tr7-10, a Potion and 8 Ruined Markets)
Play Tr7-Tr8:
- Play Bm6 twice, buy Contraband and Duke, gain 20 cards (Br9-10, Wt4-6 and 15 Potions)
- Play Tr9 twice:
- Play Bm7 twice, buy Feodum and Gardens, gain 20 cards (Wt7-10, Ch2-10, 5 Silvers, Ruined Village and Ruined Library)
- Play Tr10 twice:
- Play Bm8 twice, buy Silk Road and Fairgrounds, gain 20 cards (Up5-10, 4 Silvers and 10 Curses), reveal Wt2, trash 10 Curses
Play Bm9, buy Squire, gain nothing
Play Bm10, play Potion, buy Vineyards, gain nothing
Now we have 5 Actions, 31 Buys, and 200 VP from Goons.
Play City, draw Squire and Contraband
Play Grand Market, draw Silver
Play Bazaar, draw Silver
Play Festival
Play Inn, draw 2 Silvers, discard 2 Coppers
Play Market, draw Silver
Play Tribute, discard ChBr, get +4 Actions
Play Worker's Village, draw Silver
Play Crossroads
Play Hamlet, draw Silver, discard 2 Coppers for +1 Action and +1 Buy
Play Pawn for +1 Action and +1 Buy
Play Squire for +2 Buys
Now we are up to 15 Actions and 39 Buys, so we can:
Play Br2-8
Play 8 Ruined Markets
Play Contraband
This gives us 55 Buys and all card cost $10 less, letting us buy 8 Provinces, 8 Duchies, 8 Estates, 12 Platinums, 11 Golds and 8 Colonies, gaining 51 cards (19 Golds and 32 Silvers), emptying the Supply.
This gives us a total of 1036 VP: 750 VP from Goons, 160 VP from Colonies/Provinces/Duchies/Estates, 44 VP from Vineyards (133 Action cards), 34 VP from Gardens (340 cards), 18 VP from Fairgrounds (45 different cards), 13 VP from Feodum (40 Silvers), 9 VP from Silk Road (38 Victory cards) and 8 VP from Duke (8 Duchies).