It just occurred to me that with events like these on the board, Possession really lets you mess with your left opponent in ways that are even meaner than using up their coin tokens.
For example you could move their Lost Arts action token from Smithy to Chancellor (after having just brazenly taken advantage of all those supercharged smithies yourself)
If you possess them super early, you could cause their Estates to inherit Ruined Village-ness and well that's not nice.
Of course you always want to do a Borrow on your last Possession and make their next turn as if you just minioned them after the Possession
Additionally, you will have called in any Reserve cards they were waiting to play...
Possession already isn't exactly a favored card of many people, and man I can just see that dislike growing with this expansion in play.
Something to be aware of. I guess going forward, when Possession shows up in the kingdom along with Adventuresy-stuff... take a deep breath folks. You know it's probably going to be one of those games, so be a sport and ehm try to give as good as you get.