Files with mpz extension are used by the Moove, which is an on-line service for creating 3D avatars. They include resource description data.
MPZ file extension - Moove resource description file
What is mpz file? How to open mpz files?
File type specification:
The mpz file extension is associated with Moove on-line service that allows users to create 3D avatars and chat in the 3D Virtual World The .mpz file stores resource description data.