With widespread use of the Internet, Massively Multiplayer Online Games (MMOGs) are becoming increasingly popular. As MMOGs scale up, conventional Client/Server (C/S) architectures exhibit various drawbacks in scalability, reliability, and redundancy. This paper presents a new Peer-to-Peer (P2P) MMOG design framework, Mediator, using a super-peer network with multiple super-peer (Mediator) roles. Mediator is novel in integrating four elements: a reward scheme, distributed resource discovery, load-management and super-peer selection. The reward scheme differentiates a peer's contribution from their reputation, and pursues symmetrical reciprocity as well as discouraging misdemeanours. A deadline-driven auction protocol is proposed for distributed resource discovery. Furthermore, both common-peer and super-peer workloads are approximately balanced using a two-level load-management scheme, and super-peers are selected in a flexible policy-based way. In this framework, the functionalities of a traditional game server are distributed, capitalising on the potential of P2P networks, and enabling the MMOG to scale better in both communication and computation. A proof-of-concept prototype of this framework is described, and ongoing work is discussed.