There currently is one option to travel by night train from Odense (Denmark) to Ústí nad Labem (Czech Republic), taking between approximately 9 and 10 hours: Namely the RJ 387. These lines are operated by DSB, Deutsche Bahn and České dráhy.
DSB (Danske Statsbaner) is Denmark's national railway company, operating passenger trains across Denmark as well as connections to neighboring countries.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night.
These trains only have first and second class seats. The cars remain lit throughout the night and the seats cannot be reclined.
České dráhy (ČD) is the Czech national railway operator, running domestic and international passenger trains connecting the Czech Republic with neighboring countries.