First of all, congratulations on promoting such a cool idea for a jam, Keith. =)
It was so challenging and compeling that here I am, talking about the first game I've ever designed in my life (with the exception of D&D campaigns, maybe).
1. We've started everything by agreeing upon some designing principles. We wanted it to be quick, versatile, simple to understand but with things to be learned, strategic without being 'solvable' and casual without being 'dumb'. These were the five goals that guided us during the development cycle.
The first fundamental gameplay aspect decided was the core mechanic: the two condition cards (which eventually became day/night and hot/cold). It was the solution we've came up to in regards to how we could make the game strategic and dynamic without using too many cards nor making it too complex for casual players. After that we've came with idea for seven cards: one neutral, four that would be conditionaly tied to the first two cards and two that would change the current active condition. So then, already in day one, we were testing our 9-card game. It was not enough to have a proper game, but we could already sense the 'gamefeel' and testing match ups between different cards under different conditions felt fun in a way that seemed like we had more then 9 cards. After that we developed the remaining nine cards (including two special cards because we wanted to have something that felt like a higher layer of gameplay to please less casual players) and tweaked the numbers until it felt somewhat balanced and fair.
We wanted it to be a game that felt customizable, so when it came to the art direction and theme, we've decided to aim for something that would be quickly relatable and that could allow for player projection without feeling too generic. We wanted the cards to be as devoid of text as possible (eventually during playtesting we've decided that the special cards seemed to be the only ones that really needed the text explanation on them), pretty to look at (without taking to much time for us to design and produce), somewhat color-coded in a way that could help players create strategic associations without directly telling them, simple to understand if you know the rules of the game and educative if you don't. The theme of wizards and magic is already a somewhat established trope in roleplaying and we felt that it could help us communicate to the player that he can add new things, iterate over it and create narratives to enrich the gameplay experience.
2. I think we've reached most of the initial intended goals. The game was fun to play, we could come up with several different ways to play it and make it always fresh, both experienced and inexperienced board and card game players understood the mechanics quickly and had fun playing it, the game had a satisfying balance between luck and skill and we've managed to take some important notes for possible upcoming versions. There were however some important points that we've left out due to time constraints. The manual was written on the last day (in less than two hours to be exact) and it is quite far from what we wanted it to be. The game is simple and very easy to learn when physically played or verbally explained but the written instructions are not as clear as we desire. It also does not contain the text description to the game modes we've developed and tested, only the original base from which we derived them from and it was also written in a very rushed fashion. This is our main point of attention that we want to get right in a next opportunity and to fix in the next update.
3. Our initial intention was just to participate in the jam and finish the project within the deadline, it is our very first game after all.
But I must admit that we were very positively surprised with how fun the game turned out to be, specially when playing with friends. It was very fullfilling to see our less nerdy friend ditch her Uno and have a blast playing Manaduel as well as seeing our most geek D&D-playing friends turning what could be just a simple "who has the highest number" into a thrilling roleplaying experience or to grab the cards for about half an hour to study the relations between them or remember the most gamechanging plays. And due to that, we feel that it would be unfair to just let this idea die where it is now. We will make some updates and see what people think. =)
We will very soon (probably in a couple of days) upload a new version of the manual, closer to what we've originally intended. In this new version, we will present some of the several game modes we've developed and maybe some fun suggested game lore to accompany them. We will also focus on create more and better graphical elements to make the rules clearer as well as simplifying the written explanations.
As a way to pay homage to its origins (this game jam) we will try to always keep the 18-cards core, also because the game mechanics were so tightly built around that exact number (16 playable cards and 2 condition cards). But as a way to keep it fresh and make it even more customizable, we intend to periodically release optional expansion packs focused on additional game mechanics that the players may choose to add to the game in order to make room for more complex gameplay (ex. we've already drafted a version based around moon phases - each producing different effects on the cards when the time condition card is set to night).
Other plans such as making a playable HTML5 version, going from vector-based art to illustrations and opening a patreon or kickstarter would be really cool, but of course it depends on how well the game is received and if people will care about it, since there are many better things out there developed by way more competent people. But we hope you all do and nothing would make us happier than to be able to provide at least an hour or two of fun for you and your friends with our game. <3