If a reaction card is played when a player gains this card from an attack...
I've thought about it for an unreasonably long time, and concluded that the situation you have described never happens. I thought for a moment it was when anyone in the game reveals a Watchtower, Horse Traders, or Secret Chamber, or when an uninvolved third player reveals a Moat... but none of those cards get played.
If you change "play" to "reveal", then in 2P games it amplifies the power of a reaction card without you even having to buy/gain it, and in 3+ games it has some weird ass political effect that you clearly didn't intend. What did you actually mean?
...put this card in the attacker's discard pile instead.
This sounds like you're trying to make a card that turns an attack back on the attacker (although I'm really not clear on what it does). You have read the guides so you know well why Dominion has no such cards: it's either too weak to be worth gaining, or it's strong enough that it makes it undesirable to buy any Attacks in the kingdom, or it's "balanced" perfectly in the middle where you don't want to gain that card
or attack cards.
If I understand your current rules, it's a curse because you can gain it from someone playing Witch. Then here's how the equilibrium works:
- Any rational player would gain a curse named Familiar (not to be confused with the Alchemy card named Familiar...?) in preference to a curse named Curse.
- So cards like Witch now give out 0VP curses with some sort of benefit, instead of -1VP curses. The benefit might even (in some hard to define way) cause the card to clutter your deck instead of your opponent's.
- Therefore, Witch does not have its intended effect anymore. So nobody ever buys Witch, or Sea Hag, or the other Familiar, or...
But enough of that. You've read the Secret Histories so you already know this.
When do the two effects of Sloth (the one that's a Lab on the start of the turn) happen? If they're both on the start of the turn, then (as you know) the line you put between them is incorrect. It's also unclear what order they stack in when you have two of them, and what order they stack with Duration cards. It probably triggers the "player chooses the order of simultaneous events" rule, which is hella confusing here.
Also, it refers to the order of the discard pile, which (as you know) is not a possible mechanic of Dominion. To use it, you'd have to deliberately order your discards. Every turn. Possibly multiple times per turn. Just in case a Sloth comes up in your next hand.
And... you seem to have made it cost $0. As a trashing Lab, it's got to be worth at least $7. As a trashing Lab that multiplies itself... it's probably so strong that it's uncostable. And it's somehow a Curse...?
Greed is an improvement over Lust. But you have it at the same cost as a Silver, and I think it can't beat Silver in any reasonable situation.
It only gets you more than $2 in really, really terrible hands. You basically can't buy provinces with it because it has anti-synergy with other money. If you get a card-drawing engine going, you
might be able to turn it into a lame version of Bank, with all the drawbacks of Bank and less money.
We can make something of this card. Here's a drastic suggestion that might swing it the other way: put a buy and a coin on the card itself.