What the achievement asks
Destroy a hundred Corruption Tumors in Uldum or the Vale of Eternal Blossoms during Black Empire assaults. Ten points, account-wide, both factions.
Only during one of the six assaults
The tumors do not exist outside a Black Empire assault. Not during Amathet Advance, not during Aqir Unearthed, not during the Warring Clans or the Endless Swarm, and not between assaults.
That single restriction is the whole difficulty. The Black Empire assault is shared between the two zones, so it runs in either one only half as often as an ordinary assault runs in its own zone.
When a Black Empire assault starts, this is what to spend it on. Tumors are common inside it and a hundred does not take many assaults, but you only get the chance every few days.
What else the same window gives you
Three other achievements are locked to the same assault and can be worked on in the same visit:
- Combating the Corruption wants ten kinds of corrupted creature, all of which spawn during it.
- All Consuming needs Consuming Maws, which appear only where N'Zoth is attacking.
- Uldum Under Assault and Defend the Vale both need this assault completed once in their respective zones.
Doing them in one pass rather than one at a time is the difference between a fortnight and a month.