Casual creator software lowers the technical barriers to creative expression. Although casual creation of visual art, music, text and game levels is well established, few casual creators allow users to create entire games: despite many tools that aim to make the process easier, development of a game from start to finish still requires no small amount of technical ability. We are developing an iOS app called Gamika which seeks to change this, mainly through the use of AI and computational creativity techniques to remove some of the technical and creative burden from the user. In this paper we describe an initial step towards this: a Gamika component that takes a level designed by the user, and tweaks its parameters to improve its playability. The AI techniques used are straightforward: rule-based automated playtesting, random search, and decision trees learning. While there is room for improvement, as a proof of concept for this kind of mixed-initiative creation, the system already shows great promise.