As electric utility systems around the world continue to move towards open, competitive markets, new players, new rules, and new behavior will keep emerging. Competition not only increases the number of players in the electricity business but also affects their behavior. In this context, the need for new modelling techniques becomes more obvious. MASCEM, an agent-based simulator, can be a valuable framework for studying new electricity market entities, rules, and behavior and analyzing their possible evolution. MASCEM permits combinations of bilateral trading and pool markets. It also takes buyers' strategic behavior into account, which is uncommon in similar applications. It includes emerging entities such as traders. The simulator offers strategies and a scenario analysis algorithm for defining bids and includes models for the new players in the market, such as traders, providing greater insight into the market's evolution.