Alright, so I am running a campaign where everyone lives in fear of the Lich King, he has been assembling the monster races and, against all odds, has somehow managed to unite them under one banner. But what they don't know is that the Lich King is actually uniting the monster races not to fight the standard races, but to unite the two against a greater threat.

So, what I need help with is creating that greater threat, I am aiming for a gurren lagann style twist where the big bad is actually a good guy who is aware of an even bigger bad. Thoughts?