Launch -
Dracthyr, split into three groups, one joined Alliance, one Horde, the other became a faction of mercenaries trying to emulate what they thought Neltharion would have wanted. Wrathion accidentally released Razageth, one of the Primal Dragon Incarnates, an elemental foil to the Titanic Dragon Aspects.
Tier 1 -
We kill Razageth but as she dies her lighting overloads the prisons of the remaining three Primal Dragon Incarnates.
You have;
Iridikron - The Leader of the group, Earth Themed but known to have struck an unknown dark bargain in the past. He is the one who schemes.
Vyranoth - The Incarnate of Frost/Ice. The least fanatical of the group.
Fyrakk - The Incarnate of Fire. The most fanatical and the least stable of the group.
Patch between tiers -
We discover Primalist attempting to take over the Ancient Bough, with its portal to the Emerald Dream. We eliminate them. The Dracthyr mercenaries were lead on by Iridikron to discover the location of Abberus, Neltharion's secret lab. While leading them on Iridikron obtains some kind of artifact related to the Void. The artifact literally stares back at him.
Tier 2 -
Once the way was opened Fyrakk used the caverns around the labs to bath and enhance his abilities with Shadowflame Fire before retreating at the behest of the other two incarnates. We know now this was so Fyrakk could burn the world tree and most likely prevent the Titanic Aspects from regaining the powers they lost to the Cataclysm or stealing them from the titanic aspects. The Dracythr led to this location by Iridikron either died trying to emulate Neltharion, retreated to the Azure Span, or joined the Titanic Aspects.
Patch between tiers -
Iridikron bargains with the Infinites to empower himself or the artifact he previously gained in the hunt for Abberus and after winning his fight goes through a portal with a Void being taking the shape of a Night Elf. After the mess created by Iridikron is cleaned up he is missing but Fyrakk, who is becoming further unhinged, decides he is going to disobey whatever plan Iridikron had made and burn the entire planet, not just the world tree, himself. Vyranoth rightfully realizes mans gone bonkers and tells Alexstraza the enemy of my enemy is my friend blah blah blah.
Now you are caught up.
Edit: Formatting.