Young witch is one of the very few crds whose value is most variable from game to game. it really really depends on that bane card. We've had games where you get a fishing village bane, and the card is basically garbage. And we've had games where herbalist is the bane and...
Well, I actually think the first place you want to go here is, how strong is Young Witch if you ignore the bane. So, if there were no bane. Which will be the same thing you get if the bane isn't bought. Young witch is VERY strong here. Hands-down better than sea hag. In fact, if there were no bane, it would undoubtedly be the strongest $4, and actually pretty squarely the best card in the game, to my mind. Yeah, it's that good.
Now, even in those situations, it's sometimes skippable. Number one is the other card that would have a really strong case for best card in the game, ambassador. But also, decent trashing and a good engine, you can maybe skip it there, too. But very little else.
Why is it so good? Well, look at witch. Witch is super super powerful. I think it's the best curser in the game, and as cursers are in general like the best class of card, it's quite near the top of all cards in the game (yes, yes, you can make a reasonable case that mountebank is better - it's board-dependant). Anyway, baneless young witch has some pros and cons compared to witch. You have to discard 2 cards. Now, this makes it weaker, but... well, early, this doesn't really hurt all that much, and later, you have so much curse slog, it still doesn't hurt THAT much. And the big difference is that it is 1 coin cheaper. And the most important 1 coin. That's huge! You can just get to the YW faster, meaning play it more, meaning win that curse war pretty convincingly, and the game follows, in the heads-up, and really any matchup.
So, I think there's this notion that very often YW is ignorable, and this is just, well, virtually never the case.
But we have to look at the bane cards, now don't we? If we look at the other extreme for a moment, if the YW is always blocked, it's a pretty lousy card. Not totally worthless, but... well it's a terminal mini-sifter. You'd definitely do better with warehouse. Or about a billion other cards. Of course, even in situations where the bane is good, you generally can't rely on 100% blanket blocking. So YW has some utility even here. Not necessarily enough to get, but some utility.
And now we get to the heart of things. Middling Banes. Let's pick on woodcutter here as an example. What are your options on a 4/3 split? YW/Silver, YW/Woodcutter, Woodcutter/Silver, Woodcutter/Woodcutter. You can play Silver/Silver but I would not suggest it. Of course, there might be some other important cards, so go ahead and open amb, and maybe chapel. But let's assume there's no ambassador or other important cheap cards, for the opening anyway, at the moment.
Things get extraordinarily complicated here. Thing is, we know that W/W is a bad opening against, say, BM. So if you do that, can't they just react by playing more of a BM thing? Sure. If you open YW, can they get an advantage by going W/W? It depends on how well the draws go, probably. If their Woodcutters avoid collision, then it's probably pretty good for them, because not only are they not colliding, but they're also pretty protected. But this is pretty unlikely to hold up for so so long. Which leaves us with YW/W vs YW/S. Well, how often do you want a moat with witch?
Probably I think you should get the bane pretty often - you get crushed without it, if not mirroring anyway. But even more often, you want the Young Witch. So I think pretty often you end up going for more actions than you're probably normally comfortable with. Of course, lots depends on the specific banes, and on what's on the rest of the board. But winning the curse split is MASSIVE.
Okay, one more hypothetical case study I want to look at. Sea Hag with YW/Mediocre to bad bane. Well, thing is, people will say Hag is better. But the only way this is true is if there's an appreciable chance at a bane block. So what do you do? Well, I would probably open with the hag. I'm not sure whether it's right to get the bane or not (say it's a woodcutter again). Probably I wouldn't, because I want a second curser. If THEY go for the banes, follow up with second hag. If not, go for the YW as second curser.
Here's where the intricacies come in. If they play straight hag, you're better off going with YW. If they play YW, you're better off with Bane/Hag. But you're better off with just Hag than Bane/Hag, if they don't get YW. So it's all about timing, and when is it too late for that bane to do you enough good, and when is it enough of a problem for them to have to get the bane to make YW-Hag worth it.
If you were expecting some kind of fully comprehensive strategy, well, you're gonna be disappointed. Because the card's just too complicated. For me anyway. I hope this helps though.
Works with:
Tunnel
Weak banes
Doesn't work with:
Ambassador
Good trashing with a good engine
Strong banes