I wonder if this is a kingdom where Ambassador is skippable. With no way to increase hand size, engine potential is limited. VP chip cards like Bishop are good against Possession, so I'm not very scared of Possession either. Also, if your opponent is pseudo-trashing with Ambassador, then you can play Bishop freely and he won't trash to it.
Edit: On the other hand, playing 5 Bazaars, then Ambassador on a Curse (returning 0 to the supply), Bishop on a Gold, buy a Gold... is scary.