So here is my tactic for 40 wave survival Badge.
1. Healing is most important, I use Cleric (heal+all, revive, purify, smite, 6 in BENEDICTION),
Trying to get full Power regen equipment ( 30+ per turn) and stun resistance.
Im supporting healing with my Ranger . At the very beggining, he cast Nature Balm and Swiftness on everyone.
We need front row character. I choose Warrior. We need Inspire and Adrenaline. The last is Conjuror or Mage, Conjuror is safe pick, revive in the case of unexpected, give us two mobs and great defense buff . Mage will speed up doing achievement. If we choose Mage i would give Warrior a shield cause he will be only front row target.
2. Cast all buffs on the begin. All have 100% poison resistance, very much stun resi, high power regen, we can survive everything. The only problem is that sometimes enemies cast debuffs like Damage Reduction, if we can we should all time cast Heal on target (even if he is full hp), and pray for benedection proc. Good luck