If you play co-op, you turn is never really your own. Your allies may attack whenever they are ready, and special fast cards may be played even if it isn't your turn. No need to zone out and stop engaging with the game when you've done your thing, because you always have some options in hand to help your friends out during their turns. 

Your choice! Each of the 5 enemies in Towards Tandemera has their own unique deck and gimmick, and requires a different strategy to be beaten! You can fight against them in "normal mode" for a casual experience, but every enemy also has their own set of unique challenge rules that increase their difficulty. These rules can be used independently from each other; if the vanilla boss is too easy for your liking, use a few. If you want an insane challenge, use the entire list!