Cleric skills: Heal all, Smite(use it wisely(ex. to finish tough guy), good to use vs undead liches), Revive (second revive in a team is good, but I died only 1 time in first waves lol), Holy Light (great skill vs lots of opponents, it reduces all enemy accuracy on 30%, adding great chance not to receive damage at all)
Ranger skills: Swiftness (perma boost to all on Quickness, you can start wave with at least 2 first attacks, which can help you insta-kill even 2 of them), Pierce (can damage 2 enemys in a row, another AoE skill is good), Hunter Prowess (110% of damage and 10% chance to insta-kill)
You can took Envenomed Weapon to add a lot of poison or put 1 more point in passive "nature lore" (it's like critical strike).
I did it! 40 waves. I took Warrior, Conjuror, Cleric and Ranger.
Warrior in a center of 1rd row, others could be in different ways.
Conjuror should have skills: Mana Sprite (very helpful to restore energy and to disctract attacks), Eldrits Aegis (damage resist to all teammates for all 40+ waves, expect when some teammate die, you should cast it again for him), Banish (good when neophyte transforms) and Call Soul (to revive).
I took passive damage for summoned creatures (mana sprites took 2 attacks before die in most of cases, so I think extra health for summons is useless)
Warrior skills: Inspire (perma damage on all teammates), Cleave (very helpful when 3 enemies in a row), Execute (use it ONLY on full energy on tough enemy except "instant death immunity).
Passive: Leadership (with this you have % chance to second attack from your teammate).
Looks like I should place elevators on the sides of the mall, so NPC won't stuck in elevators (in previous attempt I put elevator right in the middle and everyone stucked in here)