Machinations Ruleset Generator (MaruGen) is a semi-automatic system for the generation of mechanics, rules, spaces (environments), and missions for video games. The objective of this system is to offer an expression mechanism for the video game designer role based on the definition of rules, and the ability to explore the concepts of progression and emergence in video games by using a formal, usable, and defined tool to design games with innovative and complex elements, and behaviors defined from combinations of basic elements. Based on the expressed designs and with the participation of programmers and video game artists, MaruGen allows the generation of agile video game prototypes in the Unity game engine. These prototypes can be analyzed by the entire workgroup to look for games with diverse complexities that make them attractive to their users. MaruGen is based on the expression of rules on elements of interest in video games and the rewriting mechanism using L-Systems for the generation of procedural content. MaruGen was evaluated in the construction of the Cubic Explorer video game and tested by gamers and video game developers during the Game Jam Ludum Dare 38.