The second area in the Challenge Hall is quite a change compared to the first.
Your team will start with a number of Walls played out. They are nice to have, and will dispose the first creatures arriving. Empirically it not worth trying to save them too hard unfortunatelly, but get good use of them until they are destroyed. Remember if your party use Lizards, they won't be able to pass your own towers until they get destroyed!
The change in enemy is also quite noticable. Aside the "normal" units what should mean no real surprise to anyone (like archers), the AI has a good amount of fire-breathing Dogs, and to make your life miserable a very noticable amount of Lizards, including some with Armour 3 ability.
For this low-level parties, who just unlocked the area should get one player with an elemental damage dealing specialized deck, while the others just use a regular strong deck.
Rush is hopeless here of course. Wait and accumlate cards during the first turns, sending out only sacrifisable things, or placing behind the double-towers some archer units (anything with Heroe's Bane ability is also good there).
The AI's spells are more area-effective, thus damaging less, making it less-annoying then Litle Jacob from Shimmering Cave. The biggest problem is ment by the creatures' high physical resistance and area-damage (of the dogs).
Ranged units are advisable against the Dogs. Watch out, as some of the creatures have Vigilance ability.
With a team of three lvl 30-35 Heroes and fast-moving creatures (mostly Halfblood, including Chief Hrafn) we managed to beat this challenge, but it depended a lot on Real Life Luck, so unless you have really high-tier decks, from this point all challenges demand "all four".
The "Win"-status is usually achieved by finding a niece on the defenses of the AI, and then filling up the avaiable summoning-spots for it, and not after it runs out of cards.