For any reason this area is again about random encounters with undeads (read the story for more details).
The Undead race, or better called faction is infamous about two things in general: easy source of elemental damage and respawning (in various forms). This makes it hard for you to resist their damage (and believe me, Pegasi, for being flying cavalry, are not that great of counter against them), or to advance in the lines. And while their damage per hit might not look that awesome, with all their resistances they'll accumlate that damage on you fast (especially with their many ranged units).
The Undeads also not lack Vigilance ability.
The first two campfire have Ghosts as primary problem. They deal ranged elemental damage. Fortunatelly the AI has always low amount of cards in its deck in this area, so at least there you have an advantage. This stage will likely go away fast, especially if you could finish the final fight at the previous area ;)
The 3rd and 4th campfires have Bats. Bats can cause some poison damage (these bats are still low, so no 5 shadow damage per turn yet), and their most fearful ability is Flying. They have low charge-count, and while not cause too much damage, they can fly over your creatures, soon filling up your spawning-pods if you are ot careful.
But they can be finished without flying units if you can send your units close to each other, as Bats are not cavalry, can only advance 2 hexes in a turn. Knockback ability also might provide the necessary edge in these combats.
I personally liked combining Lizards with Feleses and Werewolves for the bats.
Against the ghosts any decent damage, middle-HP units can do - the only thing you need is range/speed to reach the new creatures played out.