I discard a Vineyard; the other guy discards an Estate. How many cards do you draw?
Ive seen you give this same answer to so many fan cards dealing with card costs.
The answer is probably the same, cost in coins, ignore Potions.
That's how I'd resolve it too, but the wording of this card doesn't lead to that conclusion. The Alchemy rules specifically state that (for example) $2 is neither more or less than $P. That definition is important for cards like Remodel and so on that require you to know what set of cards are "less than" some arbitrary cost. Apply the Alchemy rules to this card, and you cannot produce an answer to the question of whether Estate or Vineyard is "cheaper."
The way you'd fix the card would be to say, explicitly, "cost in coins" (which is what Bishop, Trader, and Forge do).
Yeah, like you said, "adding cost in coins" should remove Potion confusion.
About the card itself:
These kind of "cheapest" or "lowest" cards are difficult to make because early game they are very weak/powerful and in the end game they are the opposite of what they originally were. The strength of the card also varies on the number of players.
I'd throw in a "Everyone draws a card" to the beginning of the discard thingamajig. And change the bonus to: +1 Cards, +1$ and make it a cantrip.
Gives it a powerful no discard bonus, and everyone else has the option to shut down your engine, but then again your helping them out with the card draw
Maybe add a little blurb at the bottom saying "While this card is in play, at the end of your buy phase, if no player discarded a card to this, everyone else discards down to 5 cards in their hand".
That might need a re-wording, but you get what I mean. It also adds some mystery "Is this the last one he'll play? Do I risk a card? If I don't I'll lose all the cards I've drawn..."
Actually, I have an idea that is a spinoff of this card:
Gambler
Cost: 5
Action
+1 Card
+1 Action
Every other player draws a card. They may discard a card from their hand.
If no one does, +1 Card, +1$
While this card is in play, at the end of your buy phase, if no player discarded a card to this, everyone else discards down to 5 cards in their hand.The named seemed appropriate for this card. It's a gamble for you, if they discard a card or not, and it's a gamble for them, If they
don't discard a card or not.