Board Thread:General Discussion/@comment-4854965-20160209020038/@comment-35239568-20180407095113

The best guesses are his name is mason. It follows the stanFORD and stanLEY pattern, and since it was confirmed Mabel is 10 minutes older than dipper, just as Stanford is older than stanley, it would make sense following alphabetical order (F goes before L, and B goes before S.)