Well, we can hate on Possession instead of anything else, but Pirate Ship is still getting an errata/ruling about what it means to take the tokens.
Pirate Ship needs errata to deal with Guilds.
Right, I see. Now Pirate Ship says to take tokens and put them on
your Pirate Ship mat, so you can't get them with Possession (for the same reason you can't get VP tokens following the Prosperity rulebook).
With Possession and tokens, it seems like everything has to be ruled on specifically anyway. Even +1 VP is defined in the Prosperity rulebook as a player taking a VP token and putting it on his mat. Going by this, Possessing you will only let me take VP tokens and put them on your mat.
There are no VP mats in Empires.
But that means you
are changing how "+1 VP" is described in the Prosperity rulebook. I mean, someone could have Alchemy and Prosperity, but not Empires, and play with someone who has Empires (or in a tournament where the errata are known), and if they play with Monument and Possession that person needs to be told
both about the Possession errata and about the change of how "+1 VP" works (i.e. not put on your mat).
Yes, all your -$1 tokens (you could have several!) would trigger and all of them would give you $1 less. Is there a general rule that you can't go below $0? All other coin reduction abilities specifically say so. In any case you lose all your -$1 tokens.
Bridge etc. specifically say that they don't reduce costs below $0; it's part of their effects, not part of the rules.
Tentatively playing Copper with two tokens will only remove one token. The token specifically does not interact with getting $0. Once one token has been applied you are getting $0.
I don't understand how getting +$1 don't just trigger both tokens? "When you get $" happens for both tokens, and then you resolve them in an order you choose. That's how abilities normally work.