There is a potential issue with priority, especially with "In games using..." or "While this card is in play..." clauses.
Consider a duration card called Barricade. While you have a Barricade in play, you cannot gain Curses or Ruins. Now, there are various ways of gaining. Presumably if an opponent plays a Witch, you won't gain the Curse. Seems to be what was intended. But what if I buy a Curse? The wording looks like I could spend a bunch of buys on Curses while my Goons stack is in play, but not gain any Curses. What if I buy something that is embargoed, do I gain a Curse then? What if I buy Death Cart, do I gain the Ruins? What if I have a Haggler in play and buy a Poor House while the Copper pile is empty?
That last one seems especially thorny. Does Barricade trump Haggler, or does Haggler trump Barricade? Does it which one I played first?
The relevant rules are:
"He announces which card he is playing and follows the instructions written on that card from top to bottom. The player may still play an Action card even if he is not able to do everything the Action card tells him to do; but the player must do as much as he can." - Base game rulebook
"The instructions written on all the action cards alter the rules of the game by, for example, allowing the player to draw more cards from his Deck, play more Action cards in the Action phase, use more coins for the Buy phase, Buy extra cards in the Buy phase, and so on." - Base game rulebook
The instructions on the card alter the rules of the game, so if you buy a Curse, you won't gain a Curse. You could spend a bunch of buys on Curses while your Goons stack is in play, but not gain any Curses.
If you buy something that is embargoed, you follow Embargo's instructions. Because you can't gain Curses, you are not able to do everything Embargo tells you to do; but you must do as much as you can - nothing, that is.
If you buy Death Cart, you follow Death Cart's instructions. Because you can't gain Ruins, you are not able to do everything Death Cart tells you to do.
If you buy a Poor House while you have a Haggler in play, you follow Haggler's instructions. Because you can't gain Ruins or Curses and the Copper pile is empty, you are not able to do everything Haggler tells you to do.