Had a little bit of trouble figuring it out, so adding the format that I found here:
# wfuzz -c -z file,/usr/files/userfile -z file,/usr/files/passfile –ntlm FUZZ:FUZ2Z https://
In a nutshell, the -z coincides with the “FUZZ”. Each subsequent payload/FUZZ combination points to the FUZ2Z or FUZ3Z and so on.