Thats a little swingy…how about a better benefit to make it cost $4.
It seems swingy, and we all know that ruins and copper are better then curses. On the other hand, the card will discard your green for you - something that most of the time is a good thing (If you buy Nobles or Harems when this card is out, it's your own fault... You'd think twice before buying them if your neigbor collects Tributes, won't you?). So if others might loose the silver or gold for their next turn, or a festival, you get a better hand at the cost of a curse. It's not that unfair, is it? Swindler gives out curses for coppers, with a chance higher then 50% early-game.
But i guess you're right about the benefit. +1action is not that good, even if you can play two of them in a row. Nobody likes attacks without benefit...
It could make you discard a card from your hand and then give +2X after the Tribute-method. That would make the card itself a small counter to it. So how about that:
Iron MaidenEach other player discards the top card of his deck. If it is...
...an action card: he gains a ruins
...a victory card: He gains a curse
...a treasure card: He gains a copper
Discard a card from your hand. If it is...
...an action card: + 2 actions
...a victory card: + 2 cards
...a treasure card: + 2$
3$ Action - Attack - Looter