The conflict who set the foundation of the Crimson Legion, the alliance between Hybrids and Equestria, and Heaven’s corruption in her powers, was during Heaven’s travel to unite the hybrids, she was witness of the return of a demi-god hybrid call himself “Darkblade”, who wish to claim the hybrids for their will of obliterated the pony race of Equestria.
Eventually he was defeated, but the battle against him was terrible.