2 minor questions:
-How exactly does Fumble work? Specifically, what's the limitations on what actions you can describe? Can you just say "when my opponent would take an action" or "when my opponent would play a card", or does it have to be more specific, like "when my opponent would destroy one of my cards" or "when my opponent would play an invocation"?
-What is the intended frequency that a player will be adding new cards to their deck? Theoretically, it seems like a player could add a new card almost every duel, with "prepare for the fight" or via "Draw the Perfect Card".