There currently is one option to travel by night train from St Johann im Pongau (Austria) to Bremen (Germany), taking between approximately 14 and 15 hours: Namely the UEX 1310 operated by UEX.
UEX (Urlaubs-Express) operates seasonal night trains, including car-carrying trains (Autoreisezüge), from Germany to Austria and back.
Options range from seats and shared couchettes to private couchette compartments, sleeper compartments and connected sleeper cabins.
You can bring your car, but only between the car terminals, and you book the vehicle along with your ticket.
Skis travel free in the ski compartment. A bistro on board sells drinks and snacks.
There is a reduced fare for children who have their own seat or bed.