Designing and implementing gameplay that is fun is a hard problem, often met with subjectivity, generalizations and criticism. For the scope of this two part post, I will discuss the design of gameplay as it pertains to the player's mechanics (what the player can do) and the AI (NPCs and/or the world simulation) within the game world. In two parts, I will describe a methodology that game developers can use to formally express the design of the intended gameplay which tries to ensure a positive and fun player experience. This methodology is highly inspired from ideas presented by Paul Tozour and discussions I’ve had with other game developers. There is a wide range of material available that describe varying processes across the industry centered on designing "the fun" in gameplay. At times these techniques tend to be inconsistent or rely heavily on subjective feedback. We also sometimes find ourselves using other games to drive our design decision making. While this is an important part of game design, it is not the only way to drive ideas forward. We can and should think about what our intended gameplay could be rather than possibly limiting ourselves to previously established ideas. The proposed approach focuses on the player as a key gameplay ingredient in defining the rule-sets that then drive the design of the AI and world. This design process forces you to think about the player up front which ends up being player-centric and has a wide range of benefits. With that in mind, an apt name for this design methodology is player centric design.