Ok FYI, this is only a rough draft, and this is a little history: Long ago, before the High Elves were in their Golden Age, dark entities of immense power ruled over the Mega-Verse. The High Elves decided to start a rebellion agains these entities, to free the primitive inhabitants of the young universe. The High Elves knew they couldn't fight these entities head on, so instead of fighting, they tricked most of them into a prison, now known as Dimension X. They captured all but a few, and those few were the most powerful, clever, and ruthless. The High Elves knew they couldn't trick them, so they created weapons of immense magical power to destroy them. In the gigantic battle that ensued, the High Elves were able to slay or capture all of the remaining ones. But just before the strongest one, known as the Time Splitter, was captured, he used a mineral known as Infinite to fracture time and space, creating multiple mirrored realities, called dimensions. After this tremendous battle, the High Elves were in there Golden Age. But this age didn't last forever, and they were soon overthrown by the Forerunners.
Now, as the battle of Antares draws near, the Time Splitter has once again become conscious of events outside his prison on the Timeless Plane. Seeing a chance to rule the Mega-Verse again, he sends out his ally Hunter to find a dimension that will work as both a safe haven for the evil forces about to attack Antares, and a place where evil reinforcements can come in and help sweep away any resistance.
As I said above, this is only a bit of history. If you guys want me to continuo on this path, I will then tell you about the Dimension itself, plus tell you what these entities are. I am open to suggestions. Thank you for your help :)