Securing Deadwind Pass
After completing phase one of the quests and taking the portal to Karazhan, you find the entrance to the tower in Deadwind Pass has been overrun with now-level 110 demons from the Legion. In front of you stands Khadgar and more mages from the Kirin Tor who have simple quests ready for you (because of course they do). All of the quests in phase two can be completed solo and will just have you run around this small area of Deadwind Pass performing regular feats, such as slaying demons or turning off horrible, world-ending ley line stones.
There are six quests to be completed, but with a little help from your flying mount, you should be able to knock them all out very quickly. You can also pickup the optional Waterlogged Tome quest in the underground area near the Western Ley Line Stone for an awesome, Khadgar-filled cinematic after being returned to Dalaran. With all six quests down, you will be free to enter Karazhan and defeat the evil that has taken hold of it. Just be sure to grab the few quests from Khadgar for your trek inside, as they have some pretty sweet rewards.