What is mercury train?

Mercury Train is a fictional train featured in the game "Ticket to Ride: Europe." It is a special, one-time use train that players can use to connect two cities from their hand of destination tickets. The Mercury Train can be used to quickly complete a route and score extra points. However, once used, the Mercury Train is removed from the game and cannot be used again. This adds an extra level of strategy to the game as players must decide when it is the best time to use the Mercury Train to maximize their points.