I might try a different approach, to see what happens, but I kinda cheesed it. I'd already beaten all the little goblins roaming around, when I was trying to grind. Then I moved on to the Skyest fort, to kill wolves and snakes. I eventually stumbled onto the leader, and defeated her. This was before I got acquainted with the invasion mechanic. So I decided to go ahead, and invade Firelight. Since I already took out all the little goblins myself, I figured I'd solo challenge it, for the bonus.  After I defeat The Mountain, and make her mine afterwards (because why wouldn't I?), the screen goes black, to show me the messages that she became one of my followers. Then it looks like it does a screen change, but it just comes up black again. I can still move my characters (hearing sound effects), and the menu comes up if I call it, but everything is just black. Even if I push down and exit that chamber, the screen tries to change, but comes up black again.

As unpolished as it is, something about this game really grabs me. I hope you'll continue making improvements. And I hope you don't mind me exploiting loopholes in the game. That's kinda my thing.