I ran into this pretty nifty combo today.
It's not really rocket science and you can derive it from the title, but I'll give a short explanation anyway.
With both
Sea Hag and
Jester in play, play (with 2 actions)
Sea Hag first and then Jester.
Your opponent puts a Curse on top and immediately gains another one, because you obviously choose your opponent as the receiver of Jester's action.
Double Cursing, yay! The only drawback is that your opponent gets to discard both Curses and leaves nothing on top of his deck, but this is a minor detail.
Jester has this interaction with which you control your opponent's top card with Spy too, which is kind of like the obvious one.
Ghost Ship and Secret Chamber are less obvious, it depends if your opponent is more likely to put good cards on top of his deck or bad cards. Either is fine for you, because you get to choose who gets it. If an opponent immediately plays Secret Chamber to your Jester, your opponent will likely put an average card on top, like Silver, which is still decent.
I am mentioning all these other Jester possibilities, because I couldn't find a Strategy article about it.
Here is another combo with Jester:
Fortune Teller / Jester