Not even sure how I killed this boss that quick. Normally its a bullet sponge boss. I was playing very aggressively using 2 Fire Grenades on the boss and immediately running to the Boomshot, exhausting all that Boomshot ammo then running to the next Boomshot and doing that. I didnt even get a chance to fire the first Boomshot round before the boss died this time.
The two initial fire grenades would burn the boss' health down to about half I noticed. If I had 4 fire grenades it might burn the boss to death and kill it super fast as well. Normally the final remaining half of health takes very long to get down , even with 12 boomshots. Hitting it while its open does much better damage but I was just firing all boomshot ammo into it and trying to take out he minions with splash damage. I was also using the female teammate 's Stun Sword attack on it , which seems to make the carrier take more damage when electified. I dont know if a juvie exploded on it while it was stunned or what, but it died super fast. This is a clip from the upcoming tutorial of this mode. It will be released in 6 parts.