Grand Opening is one of the achievements in Glory of the Legion Raider, complete the Glory of the Legion Raider, you will get the mount Grove Defiler.
1. Activate all the spotlights around the Nightwell and then defeat the Chronomatic Anomaly in The Nighthold, on Normal difficulty or higher.
2. You need to provide your account.
3. Your character's level should be 45.
4. ETA: 1-3 days.