With next generation consoles, players expect more from open world games. They expect deeper immersion with AI and more emergent gameplay that will add replay value. In ACU, we accomplished this by developing non-player-centric systemic events, capable of creating spontaneous gameplay opportunities for the players. This lecture looks back at the development of the system from both a game designer and a programmer's perspective, and how we overcame some of the challenges presented by systemic gameplay via concrete examples. This talk will present the initial vision for the system, our design intentions, problems we met as we iterated on the system, and the solutions we used, integration with other crowd systems, level and mission design concerns, as well as avenues of improvement.