I'm thinking about a card which says something like "until the start of your next turn, when an opponent buys a card, take a coin token". It seems like a decent idea in single-player, but I can't solve the problems with multiplayer.
As written, in a four-player game, you'd get three times as many coins. If I change it to 'the player to your right', then it feels like I'm putting pressure on one player to play a certain way that the others don't get. Maybe that's fine, as you don't get to choose the player. I wondered about limiting it so that you divide the number of buys by the number of opponents, rounding up, but that means that by buying less the early opponents can pressure the later ones. I also thought about having it so that in 3p you don't get the first coin and in 4p you don't get the second, but then the the earlier opponents can pressure the later ones to buy less by buying more, which seems worse.
Is there a way to fix up the idea, or should I give up on it?