Knowing a boss phase where they're active and targetable for a good little while, or just any elite enemy, you can pop your Song of Swords and Howler's Immunity mods and a Dragon Heart, immediately handing out a massive damage boost and damage reduction, and providing a heal.You will rotate your weapons while dealing with additional enemies, or just helping to damage the boss, just focusing on getting your mods ready hopefully by the time they're down.
This build is very much geared towards having a carry like a Crit Build that may have difficulty in dealing with large groups or would just do better with focusing on raw damage rather than concerning themselves with healing it is very much a co-op build.
A Co-Op build to sustain and boost a carry boss-killer friend