You will have to defend a number of attacking waves and defeat the boss to clear the map. You can also choose to let the next attack phase start earlier if you do not need the full recovery break in between waves. The challenge is to finish the map as soon as possible, but you will have to defeat the same amount of enemies.
In the future there will also be a survival defense map where you have to hold out as long as possible.
Your prayers regarding the best promo card in the game have been answered! (see your topic)
As for the roadmap, I actually wanted to reply to that in a FAQ-corner at the end of the update, but ended up scrapping that area since the update was already quite big and I answered the other questions already in the past 2 weeks. (I might make a general FAQ at some point though). Anyway, regarding your question: the team has been changed quite a bit over the last month so we are still trying to figure out what the best workflow will be. Because of that we have not been able to make a clear roadmap, but in the future that will be the plan. Nothing definitive I can share yet, but hopefully in future updates I can shed more light on this.