Despite the rigour and ability of game theory to cope with oligopolistic electric markets, it fails to model many existing behaviours in the real-world circumstances. The traditional models such as statistical extrapolation or econometrics are not capable to anticipate the changes in the pattern of the market prices due to the future structural changes. Furthermore, in such free and open markets, there is a more intense need for each participant to benefit from a certain level of autonomy, while keeping some capabilities to interact, communicate, collaborate and negotiate with other participants in an efficient way. As a result, there is a need for a novel framework of modelling that could include game theoretical assumptions as well as other more complex assumptions. Agent technologies in general and agent-based simulation in particular offer this possibility. This paper proposes, in a decision-making perspective, a new multi-agent architecture specifically designed to support planning activities in decentralized electricity markets, with a certain level of flexibility. In this model, synthetic agents are created allowing flexible representations of the multi-functional market players and possible mergers and coalitions in the electricity market.