can't repeat lvl 23 2:54, but it involved taking the upgrade, being patient and rigging it so the others ran out of power
now stuck on 27. best try so far was taking orange's base
Fire tree is not a must for hard badge. Icebolt with just the basic fireball spell is very effective for clearing, and towards the end of survival you can just use it to slow warlocks while continuously healing. So be sure to put 12 points in ice for the running and mana regen passives, and 13 in divine (tiri23's continuous healing formula with full Holy Wrath). I just put the remaining 3 in fireball but one of the divine spells is probably better.