The Ticket to Ride: Mystery Train Expansion adds some cards to the Ticket deck. These additions aren't actual tickets, though. Instead, they are special cards that allow you to get bonus points at the end of the game, with the exception of one card that allows you to, in lieu of a turn, look through the entire deck of tickets and take any card you want.
One card lets you double the value of any ticket that you make (only for cards worth 10 or less), one gives you bonus points for making a cross-country route, one gives you bonus points for a west coast route and one gives you bonus points for connecting to the most cities.
This expansion is available as a free giveaway at Essen in October '04, and in the December '04 Game Trade Magazine. It should also be available to distributors, retailers, and through the daysofwonder web site when it's in print.
8 to 10 cards.