The on-play effect seems incredibly weak. If it happens to be the $1 that bumps you up from $7 to $8, and you have a spare action, then you would probably play it. But for the most part, it's a dead card once it's in your deck.
I think the on-gain effect is something that has been done on other fan cards, and I think it runs into some problems, although limiting it to only buying one Crone per turn might circumvent most of them. Limiting to only one buy per turn might also prevent some problems that tend to arise with a $0 kingdom card.
The on-trash clause is weird and you would have to be a lot more explicit about it. Where does it go if I can't trash it? Does it go back into my hand like Fortress? Or am I just not allowed to trash it at all if I can't? And if it's the latter, then what happens if I play a card that forces me to trash, and Crone is the only card in my hand? It also has the Throne Room/Moneylender wording problem of being forced to do something, but not requiring that you reveal your hand to prove that you can't do it, although that's a lot more minor.
There's a reason no cards have an on-gain (or on-trash) effect that give +buy or +coin (or +actions). That reason is that you can gain cards not on your turn, and then it gets weird. If my opponent Swindles my Copper into a Crone, then hey I gained a Crone so I get +1 buy, +$1. But it's not my turn, so what happens to that bonus? Is it saved until next turn, or does it just go away?
To fix this, you probably just want to make it an on-buy effect, rather than on-gain. I came up with a card once that had an on-trash effect that was something like "When you trash this, set it aside. At the start of your next turn, +$3 and move it to the trash pile". I think you might be able to get a similar wording to work for +coin on-gain, but I don't think that would have the same effect as what you intended.
To criticize the card itself (and not just the wording issues), I think it's a very very weak card. Most of the time, it will not be worth getting a dead card just to get $1 more to spend on this turn, especially because you (usually) have to pay $1 to trash it. But then it really changes things when you hit that $7 hand near the end when you know you're not going to be re-shuffling anyway.
So everything I've said so far sounds very negative; I hope it didn't come off as harsh. I do think that you did a good job realizing some of the potential problems with it and addressed them appropriately (limiting to one buy of Crone per turn, making it hard to trash), but overall I just don't think it would work as it is. If you really like the card, then you should keep working on it and try to fix some of the problems I mentioned. It's not necessarily a concept that can't work, but I think if this concept is going to be successful, the end result will end up looking quite different from the card you have here.
Edit: I wrote this assuming that the -1 VP was like a -VP token that you got each time you played it. As noted by Warfreak2, if you mean to make it like a Curse, you should have a line separating the -1 VP.
