Slay the Spire has been one of my favorites for years, and recently I've been using the "Spire with Friends" mod. It allows up to 6 players to link up their runs to try to win. The added Courier map location is what pulls it all together, allowing you to spend gold to send cards and relics to your teammates.

In a normal Spire run, most of your gold is probably being used to remove your basics in shops. In a multiplayer run, there is a larger incentive to hold off on doing so, since a well timed delivery can save another player from certain death.