Dragonwrath, Legendary Staff - questline overview

Right Trying to compose some sort of a quick guide of how-to get the staff once you are on the questline.

Step 0 

- Preparation. kill a T11 endboss. Any of these, Nefarian, Cho'gall or Alak'ir, will do.

Step 1 (A Legendary Engagement) 

- Go pick up the initial quest from inside the mage tower in the portal room.

Step 2

- Simply follow the quests to Caverns of time and watch a cutscene. 

Step 3 (All-Seeing Eye)

- Go kill a bunch of Firelands bosses to collect 25 Eternal Embers. 

10 man drops 0-1 per boss kill

25 man drops 1-3 per boss kill.

Also go buy 3 "Sands of Time" from uldum. Should be around 3k gold for 1. Less or more depending on reputation and guild perks.

Step 4 

- You will need to do some solo quests in the nexus area and inside the nexus. Nothing really difficult just follow the quests and you should be done nicely.

Step 5 (Delegation)

- This is where the real tricky bit lies. You need to go dig out the branch of nondrassil from Firelands.

Basically you have to fight each of the 1st 4 bosses in the firelands to aqcuire certain items.

And once you have those items there is a special encounter that needs you to combine all those items to summon it.

Here is a very good post on the forums that explains what you need to do.

http://us.battle.net/wow/en/forum/topic/2795122615?page=5#98

Also of a video of the encounter:

 

After you have killed the boss as you can see you get the branch of nondrassil and you can go and turn it in for your reward.

Step 6 

- Some more running about and quest chains

Step 7 (Time Grows Short)

- Collect 1000 "Seething Sinders". Again dropped from bosses in firelands. More RNG. Nothing more really needs to be said here i think.

Step 8 - (The heard of flame)

After successfully managing to grind your way to a 1000 seething sinders you will be given your final task to go an kill ragnaros and obtain his fiery "heart of flame"

After managing this the staff should be in your hand 

Reference: http://www.wowheadnews.com/blog=188751/dragonwrath-tarecgosas-rest-legendary-staff-quest-guide