Fighting them wasn’t too bad, it was more that I was off fighting a distant war when they arrived on boats right near my heartland, so just getting my armies back to defend took enough turns that they razed a few provinces before I could engage them. But knowing that its a special endgame thing rather than just random bad luck is good.
How long does it go on? A second wave just showed up after the first 2 factions were eliminated. Do I need to do something to make them stop? I’m playing Malekith in the Mortal Empires campaign.