Shadow of the Betrayer

As of patch 7.3.5: If you are stuck wondering where the last quests to complete the criteria of 'Borrowed power' of this achievement, then [npc=18417] in Nagrand should help you advance the story line to complete this achievement.

For Horde Loremaster (PART 2, look thru comments for part 1)

All soloed on my alt 110 ilvl 934 Guardian Druid. If you’re deciding to do loremaster later in the game like me and you’re starting the zone fresh, I highly suggest doing it on a druid because you can kill and instant fly off, makes things go by so much faster.

All I did was follow around the large bold exclamation point on the map. Sometimes the quests are mixed and it makes you run around back and forth, but so be it. This is still minimum list of quests to do, everything else is a side quest.

Go to Netherwing Fields and find Mordenai (he pats around, he was at 61.85, 59.50 for me - if he’s attacking a Flayer, kill it so you can talk to him) and take:
Kindness (kill bigger Flayers for 1 full carcass or smaller for 5 giblets to make 1 carcass)
Seek Out Neltharaku (I flew up high and found him at 64.90, 60.93)
From Neltharaku:
Neltharaku’s Tale (talk to her again)
Infiltrating Dragonmaw Fortress
To Netherwring Ledge! (the look like a red thorny plant)
*when you go to turn this in, she has flown down to the ground to meet with Mordenai. Then she flies back up and you can turn in
The Force of Neltharaku (make sure you’re no in combat when you do this - meaning dont attack the orc next to it. Use it on the dragon, dragon will turn, then kill the orc so it is free to fly off. If it is not near an orc, it will move to an orc to attack so follow it)
Karynaku
@ Dragonmaw Fortress From Karynaku:
Zuluhed the Whacked
Ally of the Netherwing
From Mordenai:
Blood Oath of The Netherwing
In Service of the Illidari
go to Netherwing Ledge->Dragonmaw Base Camp
From Yarzill the Merc:
Your Friend on The Inside
The Great Netherwing Egg Hunt (heh, I was flying around looking for one, and happen to get it from herbing Netherdust Bush)
From Overlord Mor’ghor:
Enter the Taskmaster

go east on to 74.46, 86.63 and kill Arvoar the Rapacious - he drops:
A Job Unfinished…
Netherwing Ledge completes

If you haven’t already, you need to pick a Shattrath faction
@ Shattrath from Haggard War Veteren at 59.64, 50.98:
A’dai
From Archmage Khadgar:
City of Light (follow Khadgar’s Servant, he lies when he says this won’t take long)
back @ Khadgar
*I picked Scryer

Back in Shadowmoon Valley @ Sanctum of the Stars (had you picked Aldor, you would go to Altar of the Sha’tar and it would be different quests I assume)
From Larissa Sunstrike:
Karabor Training Grounds
A Necessary Distraction (don’t accidently kill him)
Altruis
in Nagrand from Altruis:
Against the Legion (kill a Wrath Princess and then take the blood to 38.36, 18.82)
Against the Illidari (he pats around, I found him at 28.31, 50.35)
Against the Odds (use the spear to summon it)
^take all 3 together, you can do in any order
*Personally, I flew straight north and did Odds, then took Zabra’jin FP in Zangermarsh to The Stormpike FP in Netherstorm to do Legion, then to Shadowmoon Village in Shadowmoon Valley to do Illidari, turn in
Ilidan’s Pupil
The Book of Fel Names - DUNGEON @ The Shadow Labyrinth in Terokkar Forest (drops off Blackheart the Inciter)
Return to the Scryers
Varedis Must Be Stopped
Borrowed Power completes

continue @ Sanctum of the Stars
From Arcanist Thelis:
Tablets of Baa’ri (green glowing piles on the ground)
Oronu the Elder
The Ashtongue Corruptors (destroy the totems surrounding the guy so you can kill him)
The Warden’s Cage
@ Warden’s Cage from Sanoru:
Proof of Allegiance (back outside - he pats around up on the wall)
Akama (in that cave, swim down and to the right at 57.61, 47.76)
From Akama:
Seer Udalo - DUNGEON @ Arcatraz in Netherstorm - entrance at 74.27, 57.77 - hes dead on the ground in a room before the last boss
From Udalo:
A Mysterious Portent
back @ Warden’s Cage
From Akama:
The Ata’mal Terrace (kill all the Soulstealers, Shadowlord Deathwall flies down - kill him)
wait for him to talk a minute then take Akama’s Promise, turn in at Shattrath
Akama’s Promise completes

For those of you looking for this achievement don't forget the quest Illidari-Bane Shard from Overseer Ripsaw. Since it's a drop quest it's often overlooked.