King spawns are summoned during the fight with the Penance King in final wave of Barbarian Assault hard mode. If they touch the player, they explode and deal 25% of maximum health as damage in an area. If one is killed when a player is near it, the same damage is dealt. King spawns will eventually explode on their own if not killed quickly enough.
Due to their high explosion damage and very low health, it is recommended for players to take them out at range. Resonance will block but not heal from their explosion.