Champions cannot have their HP reduced below 1 point.
Since survival is guaranteed for 50 turns, your DPS champions should focus entirely on damage. Champions that apply Poison , HP Burn , Decrease DEF , and Weaken are top choices to maximize every turn. unkillable-team-raid
Even with unkillable buffs, the Clan Boss’s stun can throw off your cooldowns. You must designate a "Slow Boi" or stun target—usually a champion with high HP and low Defense—to soak up the stun and keep your speed tune in sync. Champions cannot have their HP reduced below 1 point