This ghostly enemy possesses electrical beam attacks that deal exponentially-increasing lightning damage to any visible heroes, the moment he/she gets too close. The damage caused by these beams increases by 20% per hit; it resets once the hero(es) are out-of-range. The beams never target defenses.
Harbingers will keep their distance from whatever they are targeting. They prepare a four-volley lightning ball barrage over the course of ~7 seconds, then fires them for ~4 seconds. These projectiles ignore Reflection Beams and deal splash damage on impact. On some maps, harbingers can be tricked into going around tight corners and running into your defenses to attack something far away, but getting close to this enemy is ill-advised.
Harbingers are naturally lightning resistant. A Darkness Trap or Strength Drain Aura is required to be effected by such elemental attacks. They possess a very large health pool that can rival that of ogres. In the Infested Ruins and Tomb of Etheria, two maps added with the Final Update, the harbingers are poison-based instead. They naturally resist poison and their attacks inflict poison damage as well.
Like the Djinn, Sharken, and Goblin Copters, this enemy is announced when it spawns (in dark blue text). But unlike these enemies, harbingers do not appear on non-native maps on Nightmare difficulty. However... they DO spawn on some CDT maps on Nightmare, where they do not on Insane difficulty and below, such as Coastal Bazaar.
- Deadly Striker Towers can snipe harbingers from a distance, before they get close enough to throw lightning balls or electrocute heroes.
- Harbingers are susceptible to knockback. Weapons and defenses with strong knockback, like the Chicken Baller and Deadly Striker Tower, can keep them away from heroes.
- Enrage Auras can make harbingers toss lightning balls at other enemies, but their automatic chain lightning will NOT target them instead of heroes (unconfirmed).
- Place minions in front your main damage-dealing towers (notably mage towers) to keep Harbingers away from stationary tower-buffing heroes, such as a Monk (w/ Tower Boost) or a Summoner (w/ two guardian pets).
- The Huntress' and Ranger's invisibility allows them to get up close to Harbingers without taking damage. However, they will get electrocuted if an uncloaked ally is nearby.
- Despite having difficulty-dependent map icons in color, the Harbinger's robe and hood will always be blue or green.