The second half (split the area at the middle of the number of campfires) is a very annoying part of the game, because the AI has a dangerous flying rush-deck of tengus.
This means the AI's creatures will come out fast (they are 1-2 turn charges), can fly over your creatures, and with every hit they become stronger (a reliable amount of he AI's deck have "Heroics" ability).
The only solution I found was to make an even faster cavalry-rush deck (fortunately the AI has no backstab). This was made from just a couple of key cards (heroic cavalry) supported with walls of the human race (they stop flying), some low charge-high HP pegasi, and other things to hold up the enemy until their hero gets disposed of.
This was requiring drawing the right cards right at the beggining, and remained very risky, the success depending on real life luck, every fight demanding 2-3 tries as average (each try costs 1 energy, and by this amount of tries, you'll feel the cost). But at least it is not impossible.