Set: Cornucopia
0$
When you play this, gain a card costing up to 1$ per differently named card you have in play, counting this. If it's a Victory card, trash this.
Cost: 5
This is sort of like a Workshop that doesn't require an action and can get better cards, I guess. It's still a dead card in your hand though - it's worth nothing except the card you gain later. The only neat thing about it is, if you have lots of differently named cards in your deck, you can get some actually decent cards.
Here is a problem with some of the cards in Cornucopia - it promotes having a variety of cards in your deck, but usually you don't want a variety of cards in your deck. Sometimes the kingdom really is good enough that you want to buy every action in it but that's pretty rare - fortunately, when you do want every action in it, that means you're building an engine, and that means you want Horns of Plenty to get cards for it faster.
However usually Horn of Plenty sacrifices getting a really good card and goes for two mediocre cards instead, like Workshop and its ilk, and that's not a good idea. Horn of Plenty is a little bit better but it doesn't usually work out for me because I don't have enough different cards to get up to 5 reliably. Duration cards help, so do things like cantrips or alternate treasures and such.
So if you can get some nice engine pieces, it's worth it. The one most redeeming factor of this card is that late game, you can self-trash it for a victory card. Usually a Duchy, but sometimes a Province. When you consider that it actually makes itself useful late game, unlike Workshop, its outlook seems a little bit better. Unfortunately, it can slow down your game if you're not careful about it, because it's a dead card. It's a card best played with some reservations, and I don't really know how to play it effectively.