You get bonus mission by shooting once on each card(an Ace) on every mission. Just look for a card in every mission and shoot it. 9 missions, 9 cards. I didn't understand this at first, kinda hard to comprehend for some which is fully understandable.
The first versions of this game were fun, but this one... not so much. Probably because the objective is not so much about actually crushing the castles. This is categorized as an Action game, yet I find it much more similiar to a Puzzle game.
I made it to the end of the Dungeon of Mystery. The last room was filled with gold and around 5x of the red chests, plus 10-15x normal chests. The foes were Ancient Titans - high health but moderate damage. At the end I had slightly below half health and mana left, but I also didn't bring anything such as potions, scrolls, etc before beginning the dungeon. Earned 38,000 gold in addition to the numerous items.
@trinity_enigma: Oh please, stop your whining. I've played almost 100 multiplayer games now and have only met one player who has those kred cards. Maybe I've been lucky, or maybe you've been unlucky, but all I know is that your statement regarding Kongregate going downhill is unwarranted. You probably just felt like QQ'ing in the comments.