Completed at ilvl 240 Ele Sham as Stormbringer. Took about 6 minutes and 2 seconds. Use Valeera as your healer. I suppose you can use the strat with most dps classes, just replace your weaker cooldown in place of Stormkeeper and stronger cooldown in place of Ascendance.
1. Use Stormkeeper at the opener, but do not use Lust or Ascendance yet. Use your normal rotation until he hits 75%. Just make sure to interrupt the AOE.
2. At 75% he’ll stop attacking for around 30 seconds and spawn two bugs. Pop Ascendance and Stormkeeper (should be back up) to burn them down before he starts attacking again. If they aren't dead, finish them off quickly, then go back to the boss and keep interrupting the AOE.
3. At 50% he spawns a bunch of small adds and stops attacking for another 30 seconds. Use Stormkeeper here to clear them out, this is probably the easiest part. Resume normal rotation and interrupts once he's active.
4. At 25% he spawns an ogre and stops attacking for 30 seconds. This ogre hits hard with Shadowbolt. Now blow Lust, Stormkeeper, and Ascendance. You need to kill the ogre before the boss starts attacking again or it gets messy.
5. After the ogre dies and Nullaeus starts back up, it’s pretty straightforward. Just stick to your rotation and survive until he's down.