I tried the Caspar and Mercedes paralogue, the Face Beneath, and got a Game Over. No matter what I did, reinforcements arrived and I ended up losing somebody. My Caspar is a Wyvern Lord, but is otherwise untrained (and has no Authority, so there's no battalion on him, which really hurts). I'm going to have to rethink this whole map. I initially went west for the treasure chest and to take out the demonic beast, then went north and criss-crossed in the middle section. Apparently this was too slow, because some of the enemies decided not to wait for me, and just started walking towards Caspar and Mercedes. I kept aggroing them back to me, but then other enemy troops would start walking towards them. I had Byleth fly up, and that triggered the reinforcements. I rewound time to try and avoid triggering the reinforcements, but then had no way to stop those other troops from walking towards Caspar and Mercedes, who aren't equipped to deal with them. I could take out the Death Knight, but then realized that was not the win condition, so I was just screwed.
Next time I'm going to go east and ignore that initial demonic beast, and just go up and aggro all of those people in the middle section. It might be more of a slugfest, but at least that way they won't go towards Caspar and Mercedes. Caspar can just fly out, but I have no way of getting Mercedes off that cliff, as I have nobody who has Rescue.