With all of Cairne's Totemic Slam demonstrations, we're going to have to call this place Million Needles.
Try sending Minis from separate lanes to avoid clumping together by the AoE from the boss.
For every PvE mission, there is a campaign version and a Heroic version. When you first begin the game, you can only participate in campaign missions. Upon collecting 50 sigils, you will then unlock Heroic missions.
Campaign missions will grant rewards after the first successful clear with ANY family. Heroic missions must be completed with EACH of the 5 different families in order to receive the mission rewards.