Blackened Urn
From WoWWiki
- Blackened Urn
- Binds when picked up
- Use: Summon Nightbane at the southern end of the Master's Terrace.
- Cooldown: 30 sec
- 1 sec cast
Source
This item is provided when you start the quest 
[70R] Nightbane. It is needed to summon the boss Nightbane in Karazhan.
Notes
After you complete the quest, you get to keep the urn so you can summon Nightbane again in the future. Only one person in the raid needs to have the urn.
If you destroy the urn, you can get a new one by speaking to 
Archmage Alturus outside the entrance to Karazhan.
