Orphan: The -2VP is to the player who played it, not other players.
Yes I know. My suggestion was to make this "Each other player takes 2VP". Or rather, to remove it, because it makes an already weak card incredibly bad. If it needed the -VP however, you'd still practically never play an Orphan after having a Grand Witch, which in turn means that for most boards you'd never have any VP tokens to lose when you play Orphan. That's where my suggestion comes into play: IF you needed the -VP, you should rather give +VP to other players. If you don't need them, drop them.
Witch Hunter: You nailed this one. Not a great card, but having Curses in your deck early can help by-pass the Heretic exchange requirement.
Yes, I got that much. It just doesn't look worthwile to get Curses just for this. It's okay if you had Curses either way, which in turn will happen if the board has Cursers, but then again this being in the kingdom discourages using Cursers, which means that on boards where the line could be good, people will just decide not to curse you, or curse you just enough to annoy you, but not enough for you to make good use of the Travellers. In other words, it will never be good. Unless you make Curses so attractive that you want to gain them, which makes the line lead to slow, luck driven games that depend highly on draw luck or at least drag the game out incredibly. The reason is that if it becomes good to gain Curses, people will do so, subsequently becoming incapable of buying Provinces (many Curses in hand, engines choking on Curses), and so the game doesn't end. Ultimately, piles would be depleted, but it would make for an incredibly exhausting and long game.
Mountain Hag: Also not a great card. Basically an Ambassador/Butcher hybrid. The one ace up it's sleeve though is it's ability to give Grand Witches to other players. This hopefully explains the weird wording. When and when not to do that is a hard decision to make.
I realized that that's what the "from its pile" was for. But consider that you had to wait several shuffles to get this card. Could you ever imagine passing a Champion or Teacher?
I'll try and test this set more. If I find it underwhelming I can relax the Heretic exchange condition to 3 cards and make Grand Witch -3 or -4 VP.
Suggestion: If you can, have another player (or yourself, if you play against yourself) play WITHOUT the Traveller line. Even just buying money and Victory cards should easily beat the line and be so fast that Grand Witch will have no chance. The advantage of "Big Money" as a basaline to compare the card with is that it is so trivial to play and so weak usually that IF it beats your line, you know for sure it's too bad.
Edit: Also, thank you
The fact that I have a bit of experience doesn't mean I'm always right, of course, but it means that I already know many mistakes because I already made them