Just got this mission. It is true that you need at least 15 heroic mode boss kills as well as at least one 645 follower to have this mission pop up.
Here are the followers I used to get 100%, with their ilvls/abilities/traits:
Image of Archmage Vargoth
(645) Counterspell/Polymorph. Ally of Argus/Child of the Moon/Plainsrunner.
(646) Reckoning/Divine Shield. Bodyguard/Epic Mount/Ally of Argus.
(645) Sap/Sprint. Cold-Blooded/Gronnslayer/Cave Dweller.
It's also worth noting that this mission does have a long availability timer as well as a long cooldown, which is shared with boxes with gear from lesser difficulties. I raised my followers' ilvls up early on, before getting sufficient heroic kills, so I was put on cooldown from getting a normal box mission.
This is how i got this mission to 100% with an Epic Mount Trait. (Reduces mission time by 50%)
Olin Umberhide (Epic)
Taunt (Counters: Wild Agression) / Cleave (Counters: Minion Swarm)
Jewelcrafting/High Stamina (Increases chance of success in missions longer than 7 hours) / Elvenkind
Nothing very important here, it is just a way to counter and that's it. Traits will not help you unless you don't use a Epic Mount Trait on your follower combo, in that case High Stamina ((Increases chance of success in missions longer than 7 hours) will help you.
Recklessness ( Counters: Timed Battle) / Pummer (Counters: Powerfull spells)
Combat Experience (Grants a bonus to mission success chance) / Burst of Power (Increases chance of success in missions shorter than 7 hours) / Totemist (Increases success chance when on a mission with a Tauren).
I think this is the most important in this combo, it increases chance with all of his Traits and has 2 counters, Combat experience increases your chance and Burst Of Power too since im using a Epic Mount Trait on my 3rd follower and that will make the mission shorter than 7 hours, Totemist will help because my 1st follower (Olin Umberhide) is a Tauren.
Gronnstalker Rokash (Epic)
Freezing Trap (Counters: Deadly Minions) / Disengage (Counters: Deadly Zones)
Skinning / Demonslayer / Epic Mount (Reduces mission time by 50%)
Nothing special here besides the epic mount and counters.
The most important here is without doubt Blook.
With this i hope i helped people who have this mission. Good luck on your mythic caches!
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