Ascendant Descending

For all of you wondering, yes, one shotting him works.

Those who wonder why there is dwarf icon on this achievement its simply because early on beta Ascendant Lord Obsidius and its adds had iron dwarf skin so the achievement icon kinda stayed as dwarf.

The 3 adds will channel a beam (not interruptable and while moving) that stacks the relevant debuff on anyone in melee range, even if that person is not their current target. They don't attack highest threat, instead attacking the most recent threat. Adds can be snared, but not rooted or crowd controlled.

One person needs to be assigned to kiting and cannot be near the adds. The kite path must not take the adds through the group.

Our group stacked on the boss. We had a moonkin kiting, spamming moonfire for super cheap (also keeping dots on the boss when possible). We kited in a _large_ circle around the boss, 30ish yards to either side. A warrior with piercing howl would run out every so often and snare them. The rest is just making sure the boss is taunted after he swaps and the adds get grouped up again. Body & Soul from a holy priest (potentially Leap of Faith from any priest) can help your team catch up.

The boss has a thunderclap that snares movement; this must be dispelled if it lands on your kiter, but it can be outranged. Don't bother dispelling it from others. Do dispell Twilight Corruption as this is cheaper than healing the dot.

Tracking this achieve will let you know if it fails. The text will turn red upon failure.

Finally, the boss hits like air. A dps could swap gear and stances and easily tank him. Done correctly, this fight requires almost no healing.