So in my mind I've thought up a few random ideas... I was just wanting to post them here for feedback/suggestions on names and costs (or anything else...). (Sorry if people have already thought of one, I don't want to look through pages of text)
Welcome to the boards! If you are interested in fan card design, I highly suggest
this article by rinkworks. It is probably a little bit out of date since the release of Dark Ages, but it is still a great foundation.
Medium:
Types: Action - Attack
Cost: Maybe 3?
+1 Card, +1 Action
Choose one: Gain a Curse, putting it into your hand. If you do, +1VP; or each other player gains a Curse. If they do, they get +1VP.
The uses may not be apparent at first, but if you can trash it (or use a watchtower) you can get rid of the Curse to get one VP (that's why it goes into your hand). And, if there's no trashing, give it to your opponents to clutter their deck.
As Tables said, this is too strong in general. -1VP does not hurt as much as the deck clogging, and this card would be extremely spammable since it is low cost and cantrip. The early part of the game will almost always involve spamming this as much as possible, then rebuilding.
The specific use case you have in mind with Watchtower is interesting, but may not work as intended. One thing to note is that the wording right now is ambiguous. It is easy to read the first part of the text as requiring you to put the Curse in your hand. If you trash the Curse with Watchtower, then the Curse never goes into your hand so the "if you do" doesn't trigger, meaning you don't get +1VP! I'm sure that's not what you had in mind.
But actually, even with Watchtower, the stronger choice is to attack the opponent. +1VP is not all that strong; clogging the opponent's deck is better. But if THEY have Watchtower in hand, then you would be giving them free VP! It makes it a card that you don't really want to play.
Traveling Merchant:
Type: Action
Cost: 2
+1 Card, +1 Action
-----
When you buy this, +$4.
This basically allows you to turn an extra buy into +$2. It would make something like the Woodcutter a lot better... It could also say "when you trash this, put it back in the supply" to keep them going longer, but I didn't want it to have too much stuff on it...
I agree with Tables on this one, again.
[Can't think of a card name]
Type: Victory
Cost: 3 or 4?
Worth 1VP per Curse you have in your deck.
You could buy all the Curses (or better yet, get them through the Medium), a bunch of these, and get a fair amount of VP.
I disagree with Tables about this card. I do not think a Curse-counting VP can ever be balanced. There are several problems.
First, it destroys Cursing attacks. If this card is available, why would anyone buy Witch? Those Curses are actually helpful now! But this is a minor issue. There's nothing wrong with having a counter, right?
I think a bigger issue is that it would simply be too powerful. In a 2p game, there are 10 Curses. If one player does not contest, then the VP card will be worth a whopping 10VP. Since Curses are free, both players have to go for them.
It gets crazier with more players, because the Curse pile changes size with different numbers of players. When there are 30 Curses available (4p game), you really, really have no choice but to go after this card. The lack of choice means that the card isn't so well designed.
The card is like Duke but for Curses. Duke works because it counts Duchies, of which there is a fixed number (sort of) and which are themselves not trivial to purchase. Curses are not a good target for counting.
That said, the idea is still interesting. I think the best implementation I've seen of it didn't count 1-for-1, and it was a Prize instead of a regular card. That way, the card doesn't completely negate Cursing attacks and it doesn't warp game strategy.