I can end the game on turn 3 with 7 points.
Kingdom: shelters, stonemason, nomad camp, watchtower, procession, catacombs, squire, fortress, cultist, develop, tunnel, black market
Black Market deck: young witch, baker
T1: hand: CoCoCoCoCo
spend coin token, play 5 coppers, buy stonemason(ST) for $6, gaining nomad camp(NC) on top of the deck, and procession(P)
T2: hand: NC, Co, Co, Overgrown Estate(OE), Hovel (HV)
play NC+2C, buy watchtower(W)
T3: hand: Necropolis(N), W, P, NC, ST
N, 2 actions
P->ST. Play ST, trash NC. Gain Squire(Sq), trash Sq, gain cultist, topdeck cultist. Gain Sq, trash Sq, gain cultist, trash cultist, draw cultist, Co, Co. Play ST again, trash cultist, draw CoCoCo, gain fortress1(F), trash F1, put F1 into hand. Gain F2, trash F2, put F2 into hand. Trash ST, gain Develop1(D), topdeck D1.
Play F2, draw D1, 2 actions left.
Play D1, trash F1, put F1 back into hand, gain catacombs1(C), trash C1, gain F3, trash F3, put F3 into hand. Gain D2 on top of deck.
play F3, draw D2, 2 actions left
repeat until:
play F10, draw D9, 2 actions left
play D9, trash F1, put F1 back into hand, gain D10, topdeck D10, gain C9, trash C9, gain Sq, trash Sq, gain cultist, trash cultist, draw D10, Co, Co.
Hand: W, D10, F1, 7 copper, 0 coins, 1 buy, 1 action.
play D10, trash F1, put F1 back into hand, gain tunnel, gain C10, trash C10, gain tunnel.
play 7 coppers, buy a duchy.
game ends on piles: the develop, fortress, and catacombs piles are all empty
points: duchy+2 tunnels=7 points
Please point out any mistakes I made, I probably made a few. This can surely be improved upon. I couldn't figure out a way to actually get any money out of this. The ending is a bit weird too, even with the process of just piling develop, fortress, and catacombs you can still probably do better than 10 points. Anyway, chances are your opponent doesn't have 10 points yet, so it's good to know that you can win the game on T3!