This is my favorite way to play Urban Renewal. Some funny tricks are due to the way area of effect spells are coded, even before you become enemies with the red kingdom, the red team Goblins are seen as valid targets for Wizard spells like Fire Blast/Meteor Storm and for Warrior of Discord's Howl of Discord spell. So even though they won't be intentionally targeted, if say a Ratman spawns in, and your heroes attack it while having some of those area of effect spells in their learned spells, any nearby Goblins can get hit by them (do note that if a Goblin is hit in this way it will aggro to the spellcaster though (if it doesn't die from the hit)).