Okay, well to sum up Lux the Great's revelations:
1) Konrad Curze drew his insanity from the Outsider. He staged his own death somehow, despite there being several primary and secondary witnesses to the assassination and fled to the C'tan Outsider. He is now the avatar of the Outsider, holding his essence until the C'tan Lord is released. M'Shen the Imperial Assassin sent after Curze following the Heresy was actually a Blank, and therefore somehow working for the C'tan all along.
2) The Emperor is actually the Eldar God Asuryan (who somehow escaped the grasp of Slaanesh during the Fall and was reincarnated) and was killed by Horus during the Siege of Terra. Upon discovering the badly maimed (but still living) body of Horus. Rogal Dorn recieves some sort of vision from someone telling him to force Horus to sit on the Golden Throne as a punishment, he is now holding the Imperium together despite being the one who intended to tear it down. The Emperor utterly obliterating Horus' soul seems to be some sort of fabrication and never happened. It is also unknown whose body Abaddon subsequently took back to the Eye of Terror and who Fabius Bile cloned.
3) The C'tan, being long term enemies of the Old Ones, realised that Asuryan had escaped the grasp of Chaos and so vowed to destroy him themselves. Thus the C'tan Deceiver plotted and brought about the wars of the Horus Heresy (commonly known as the Asuryan Bamboozlement) somehow, but we know it involved tricking the Chaos Gods, The Emperor (Asuryan), and the entire Imperium. However in order to achieve this, the Void Dragon had millennia before travelled to Terra, built the Golden Throne and allowed himself to be defeated and imprisoned by the Emperor (Asuryan) on Mars in order to set the stage for the entire Horus Heresy/Asuryan Bamboozlement, even though this happened millennia before the Fall of the Eldar, the Void Dragon somehow knew that Asuryan would escape the grasp of Chaos and would need defeating by the C'tan.
4) The High Lords of Terra are actually Necron constructs, and the C'tan Deceiver indirectly rules the Imperium.
5) The C'tan Deceiver was also behind the visions Magnus the Crimson King recieved regarding Horus' betrayal which ultimately led him to warn the Emperor and in the process irreparably damage the Imperial Webway and Golden Throne.
6) Tzeentch, the lord of Change, puppet-master of the Galaxy is actually just one of the C'tan Deceiver's proxy personas/disguises.
7) Ferrus Manus didn't get beheaded on Isstvan V despite the dozens upon dozens of witnesses. Fulgrim made a bargain with the Laer Daemon Weapon to spare Ferrus' life in return for complete control over Fulgrim. The head that Fulgrim presented to Horus was actually just a fake crafted by a sword. Ferrus (being a servant of the Void Dragon) was phased-out to Mars and stole the book of the Guardian of the Dragon of Mars for his C'tan overlords, he resides to this day on the Red Planet. In fact the whole involvement of Ferrus Manus in the Great Crusade and Heresy was just part of the Deceiver's grand Bamboozlement plan.
8) The Emperor (Asuryan) despite being killed by Horus, somehow escaped Terra and fled the Galaxy. He established himself as the Hive Mind and invaded the Galaxy with the intention of destorying his old Imperium because he knew (somehow, probably via some sort of vision) that the Imperium was actually controlled by the C'tan.
9) The Grey Knights geneseed comes from Post-Siege of Terra Horus.
Have I missed anything oh Great Lux?
(Seriously I love this Kid!!)