I don't think the Golden Deck does anything here, because your opponent can always turn for IGGs to kill you if need be.
If not for Merchant Guilt, I would be strongly considering some kind of BM mix of Embassy and IGGs.
But Merchant Guild gives you +buy. So we have strong trashing (Chapel), extra buy (Merchant Guild), great villages and draw (City and Embassy), and ample special stuff for the engine to do at the end (Possession, mas token gaining, Saboteur).
So this has to be massive engine where you trash down, get Cities, and turn for Possession quickly. You'll want to go light on tokens if your opponent does the same thing, though, so the mirror is tricky, and will probably come down to who is faster, and also who gets luckier Possession hands. If your opponent goes for money you can just utterly wreck them by playing the long game and catching back up off a bunch of Duchies and Harems (you'll have token reserves), and even pick up a Bishop or something.