The P38 2-8-8-4 locomotive, the heaviest and largest steam locomotive built in the USSR. Built to 1524mm (5') gauge. Only 4 of these monsters were built and although it was more successful than the 4-14-4, all were scrapped when it was decided electrification and diesels were the way forward.
There's a video of one in action available here:
>https://ru.wikipedia.org/wiki/Фaйл:Пapoвoз_П38-0001_нa_выcтaвкe_и_c_пoeздoм.webm