I had an idea for a "converter" of sorts that lets you basically use cards made for other games in your deck or mix and match. I'm not sure if it's in the spirit of the jam. My first thoughts were about basically using the cards I have in a mixed big  bo (Magic the gathering, some vampire tcg, some from a few other) and gradually including other things. Maybe even incorporating weird stuff like movie trading cards or something if I get a good idea. Then they just work like regular basic tcg cards. 

This sounds real fun! I think it's perfectly fine in the spirit of the jam, being able to convert or easily adapt misc cards can get people playing basic tcg faster so it fits!

I was also thinking of just looking through some old cards and grabbing fun stuff as inspiration from them with my own ideas and flare!

Maybe it's a Scenario, and you can bring other cards into the game and just play them alongside others? 

Undercards with this idea might get EXTREMELY out of hand. HOW THE **** DO YOU BALANCE FRISK?