Dipper and Mabel's Guide To Mystery and Non-Stop Fun: Secret Codes (Sorry this took so long, BTW.) Here are the codes I have found in Dipper and Mabel’s Guide To Mystery and Non-Stop Fun.
Disney Bill Cipher presents.
Gravity Falls opening dissection with Bill Cipher
Read Dipper and Mabel's Guide from the story Gravity Falls Secrets by GravityFalls-Decoder (Wild Cipher) with reads.