Cutpurse would work too :)
And getting a little further afield, so would Possession when their deck is Island Chapel
Actually, this gives me an idea for an extension of this puzzle that's actually pretty tricky: What is the biggest deck your opponent can have at the beginning of your turn that you can reduce to 0 cards by the beginning of their turn?
My initial thoughts:
You want to King's Court as many Possessions as possible, but not so many that you don't leave them some King's Courts to play on their Ambassadors. You'd also like to TR/KC all the Saboteurs and have them hit 3s when the copper and curse piles are empty, but since that's only 1 card per action played while Ambassador is 2 and Island is somewhere in between, I think the duplicators will be better used on those. Though let's see, you can only play 60 total copies of those two actions (20 KCs), which can only be generated by individually TRing every KC. Which wouldn't work, because you need to at least KC possession once to be able to Ambassador all the KCs and TRs you used on turn 2 and then Island the Ambassadors on turn 3. Except you need to do even more than that, because you'd also need to Island all the +actions you used to do it.
This is hard!