By 2010, social gaming had proven to be a massive phenomenon. However, the variety of game genres on the Facebook platform was very limited. Early leaders, like Farmville, set an example that other developers soon followed, leading to a landscape overrun with near-identical simulation games targeted towards casual and non-gamers. Guided by the belief that there is a huge, under-served audience of gamers using Facebook, Gaia Online set out to develop a social game that combined successful aspects of classic console games with the necessary elements of social gaming. The result was Monster Galaxy, an innovative RPG on Facebook that grew to over 20 million users. This talk will dive into the design challenges the team faced and lessons they learned, including designing for the free-to-play business model, applying insights from user and A/B testing, the need for continual content updates, and managing trade-offs to increase accessibility, retention, and conversion.