Great puzzle. But you get 3 curses by yourself. Counter question:
"What single card gives out the most curses not affecting yourself and how is this accomplished?"
(King's Court a Witch doesn't count, because these are two cards)
I get 2 curses in a 2-player game and 9 curses in a 4-player game too
I see several possibles:
Play a +buy (say bridge), buy 2 IGG
Play haggler, buy BV, gain 2 IGG
Remake two things into IGG
Thief & gain two IGG
In the first one, you deal out curses by buying not playing. It doesn't count.
Same goes for second possibility.
The third one is the intended solution.
The fourth doesn't work in a 2-player game. You will only get one
Ill-Gotten Gains and therefore only deal out one curse.
But still that's the correct solution for a 4-player game.