I'm trying to find a movie from the 70's or maybe it's from the 80's, it's a cartoon. In the beginning of the movie there's a guy playing dungeons and dragons or something like it and gets sucked into it but he turns into a dragon and has to try and find away to turn back into a human. As he goes along he meets a soldier guy and theirs a part where they fall asleep and their attacked by rats and I think and they start making noise that they can't stand. At the end of the movie there's a black dragon that they have to kill and he ends up in the shop he started in and there's the princes from the game there too.

This MIGHT be The Flight of Dragons from 1982.