I like that card a lot. You do mean "Setup: Move one copy of each Victory card from the Supply to the trash" right?
Sure. I design way more Magic cards than Dominion cards, so I'm more than capable of messing up specific wordings. "From the supply" does make it nice and clear that you don't have to go out and buy Alchemy just to get Vineyards to make this work.
For the record, the way Dominion protocol works, you would use however many victory cards you owned, but not be obligated or be using the card wrongly if you didn't own Vineyards. The only official card we've ever had where this has mattered is Black Market, where the descriptions about the promo indicate to use whatever collection you have to build the Black Market deck. Although Young Witch might be kind of like that too.
The limited demand on ownership works a bit like one of my favorite Magic cards, Spawnsire of Ulamog:
http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=193535.
Here's my setup card.
Leeches3P$ - Action
+1 Card
+1 Action
You may trash a card from your hand. If you do, trash Leeches. If it was a potion, +3 VP
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Setup: Each player, starting with the first player, takes any amount of <DEBT> and gains a third that many Leeches rounded down.
Notes: 20 copies in supplyIt's expected to be the most interesting when it's the only trasher on the board. I made it a potion card to make the Setup event more now-or-never, if it's a Bridge game or a Goons game maybe you really need to smack yourself with this thing.
The rider is a halfhearted attempt to make it relevant in some games with better trashers, you can try a golden deckish thing if your opponent greened too early, but 3 VP per potion seems like a shy costing point.