Here's a few ideas that come to mind:
Faustian Contract $3
Action
Gain up to 3 curses from the curse pile.
For every curse you gain, +$1 and +1 card
Junkyard $6
Action/Reaction
+1 Action
Action: Trash a card from your hand. Gain a different card of equal cost from the Trash Pile
Reaction: If another player trashes a card, you may show and discard this card to gain that card.
Exorcist $6
Action
+1 Action
Reveal the top 5 cards on your deck. If any of them are curses, draw those curses into your hand.
Then return any curses from your hand to the curse pile.
Typhoid Mary $3
(Curse?)/Action/Attack
Worth -1/-2 VP in your deck
+1 Card
All other players gain a curse
Commune $5
Action
+2 Cards +2 Actions -1 Buy
When this card is removed from play, either place it on the top of your deck or trash it.
In a set that lacks attacks, +buys, or gaining effects, Commune would be a dead card. Especially if there's no +buy, it would make your turns very boring, and force you to spam Ambassadors or something. Typhoid Mary allows you to open with doublefisting a cursing attack, which would slow the game down very quickly and not be fun for anybody. The +1 card would help you wade through the curses a little, but not enough. In most cases, Junkyard is useless, because your deck is full of low-cost cards and you're striving for higher-cost actions/treasures, most of the time. And no one trashes good cards either.
Good point with Commune, though I'm not sure how often those sets occur given those various constraints.
As for Typhoid Mary - yeah it should probably be increased to $4 - That way it becomes essentially a weaker Young Witch with no bane card.
As for Junkyard, I've seen people trash their province and gain a province to quickly deplete the province deck enough times that it strikes me as plausible. Heck, I've seen enough late game uses of Lookout go bad to make this potentially useful. However, given the card's cost, it probably may be worth it to make it more versatile.
Updated versions of Commune and Junkyard
Commune $6
+2 Cards +2 Action -1 Buy
You may gain a card costing up to $4
When this card is removed from play, either place it on the top of your deck or trash it.
My thinking on Commune - It could make for an very good Gardens engine assuming that either one has enough buys on the field to counteract its -1 Buy or waited before playing the first one until you have enough to gain many cards in a turn. I figured originally that there were enough +buy cards or gain cards (Like workshop which I've now essentially rolled into the card) to counteract the -1 buy downside.
Junkyard $6
Action/Reaction
+1 Action +1 Buy +1 Card +$1
Action: You may purchase cards from the Trash Pile during your Buy phase this turn. During this turn's Buy Phase, the cost of cards in the Trash Pile is reduced by $2 to a minimum of $0.
Reaction: If another player trashes a card, you may show and discard this card to gain that card.
Now it's a free action Trash Bridge that at worst is an overpriced market.
