Roboute Guilliman, first of the fallen - the Horus Heresy Alternatus.

Angron, the Red Angel - the Horus Heresy Alternatus.
Magnus vs Leman Russ, the burning of Prospero - the Horus Heresy Alternatus.
Janus
Horus Heresy Alternatus - The Loyalists:
Emperor's Children - Rylanor, Ancient of Rites, and Lucius, Captain of the 13th company during the Istvaan V Drop Site Massacre.
Iron Warriors and Imperial Fists - Fighting side by side during the Siege of Terra.
Thousand Sons - A legion reborn, the Grey Knights brings death to Daemon kin.
Death Guards - Unknown astartes defiently standing against the Traitors during the Drop Site Massacre.
Salamanders.
Night Lords.
Word Bearers.
World Eaters - Kharn bringing vengance for a father murdered.
Horus Heresy Alternatus - The Traitors:
Sons of Horus - Chaos Undivided.
Blood Angels - Chaos Undivided.
Alpha Legion - Chaos Undivided.
Ultramarines - Chaos Undivided.
Dark Angels - Chaos Undivided.
Iron Hands - Slaanesh.
Raven Guard - Tzeentch.
Space Wolves - Khorne.
White Scars - Nurgle.