There currently are a variety of options to travel by night train from Simo (Finland) to Pukinmäki (Finland), taking between approximately 10 and 12 hours: Namely the Yöjuna 266, the Yöjuna 274, the Yöjuna 276 and the Yöjuna 264. These lines are operated by VR.
VR is Finland's national railway company, operating passenger trains across Finland, including night trains connecting the south of the country with the north.