Okay so -
The Dreadlord’s manipulated Sargeras into creating the Burning Legion to scour all life from the cosmos. While Sargeras thought this was the only way to stop the Void from capturing a Titan-soul the reality was that this was just a way to put the other cosmic forces against each other in service of Death.
So far so good.
In service of that goal they presented Sargeras with Frostmourne and the Helm of Domination as a way to wage a proxy war on Azeroth via the Scourge, to open the way for the Legion to once more invade as they had done in the War of the Ancients.
This is where things get shaky.
The Dreadlord’s seem to take an indirect role in commanding the Scourge and manipulating Arthas into becoming the Lich King’s pawn. Arthas first act upon taking up Frostmourne, however, is to destroy Malganus.
From there things seem to resume going as planned as Kel’thuzad eventually opens a new portal for the Burning Legion to come through. Once this is accomplished the Dreadlord’s attempt to take direct control of the Scourge, but Kel’thuzad and Arthas both quietly rebel against them by the will of the Lich King Nerzhul.
By this point Arthas has raised Sylvanas, but due to the weakening of Nerzhul he loses control of the Scourge and of her in particular and she tries to kill him. Kel’thuzad saves Arthas and sends him to Icecrown to eventually unite with the Helm of Domination and become the new Lich King. Sylvanas meanwhile forms an alliance with Varimathras and forms a splinter faction of undead that would become the Forsaken.
Fast forward to Wrath of the Lich King.
In a twisted way, Arthas intends to protect Azeroth by wiping out all life and creating an undead army to face any threat to the planet.
Malganus, having formed the Scarlet Crusade swears vengeance against him and when we interfere with his plans he promises that we will not be able to defeat Arthas without his aid. The Scarlets killed many so their true service to Death is readily apparent, but Malganus’s apparent opposition to the Jailer’s pawn in Arthas seems strange (an indication that even as the Lich King Arthas had way more free will than he was supposed to?)
Varimathras meanwhile is instrumental in creating the Blight which is deployed at the Wrath Gate. Shortly afterwards he takes over the Undercity and seemingly attempts to once more summon the Burning Legion to Azeroth. His efforts are foiled by the Horde - or are they? Once again he seemed to be working against Arthas by creating the Blight, but also against Sylvanas in taking the Undercity, but if he really had wanted to summon the Legion he probably could have done so in secret without the dramatic betrayal. Did Varimathras fail Sargeras on purpose? If so, how do his actions serve Death?
Fast forward to Legion.
Malganus is seen once again at Broken Shore when Gul’dan wipes out the Alliance forces, but then is absent from then on. Tichondrius is a raid boss, but mainly seems to be baby sitting the Nightborn who swore themselves to the Legion. Varimathras appears, tortured and broken in Antorus, but he speaks to us of warnings about an encircling darkness and directly warns both Horde and Alliance about Sylvanas’s plans which by that point are already unfurling. He’s obviously bitter about his fate, but it seems odd that he would warn us about Sylvanas when (at that point) they’re both supposedly in service of Danathrius and the Jailer.
Now on the PTR Malganus swears his one and only loyalty has always been to Denathrius. Was Varimathras likewise loyal only to the one master, and if so, have they been working not just to undermine Sargeras but also to undermine the Jailer and his servants in some way? Is it going to turn out that Denathrius and the Nathrezim are actually going to be our allies against Zovaal in the long run?