I’d appreciate any help remembering the title of an old Russian or Soviet-era cartoon movie.
The story is about a prince and his servant, who go on an adventure to rescue a princess from a dragon. The princess's name is Vasilisa the beautiful. During the adventure, it is the prince's servant who takes all the risks and completes all the missions. I remember that during one of the missions the servant was transformed into a dog, and in another he went inside the house of an old witch. Finally, he manages to defeat the dragon by cutting the dragon's heads with something like a magical water stream given to him during the adventure, and rescues the princess. As a reward, the princess marries him instead of the prince.