Curses Harbinger is a powerful teamfight build centered around boon corruption and massive conditions damage and coverage.
Harbinger fills a damage role in a team and pairs well with a support guard or tempest as it can be vulnerable to getting focused. The majority of your damage comes from Dark Barrage and your auto attack Tainted Bolts in Harbinger shroud. Always make sure you are auto attacking in shroud to get maximum value from your quickness uptime and the damage output. Having high Blight can improve your skills. Devouring Cut will cost you 5 blight for 5 Torment and extra damage. Same for Voracious Arc but for a cost of 10 Blight.
Elixir of Ambition is a press to win button, it gives you every boon of the game and applies every condi to each enemy you hit. You want to, hit your enemy with it for really high damage and condition duration, but also hit your allies as it’ll give them all the boons your receive for the same duration. It is especially good when given to a roamer such as a power herald.
Harbinger has access to excellent area-of-effect cc abilities that make its kit quite powerful, most notably Vital Draw which is large float skill with effects similar to mesmer’s Gravity Well.
Dark Barrage offers you a corrupt, turning enemy boons into conditions. You should aim for target with Stability to try and turn it into Fear.
Keep in mind that Vile Blast has a longer range than stated and can hit enemies through walls. Because it is an AOE at the end of the projectile range, its effective range is actually the 900 range + 180 explosion radius. This can also hit enemies through terrain if they are in the explosion.
In shroud, your sources of cc are Voracious Arc, it also offers a leap, evade and potentially high damage,and Vital Draw. Vital Draw is by far your most valuable CC and can be used to secure a kill, or several kills, if properly placed. Try to use Vital Draw and Voracious Arc to bait stunbreaks before you try to float someone. Vital Draw can also be used defensively against revenants, thieves, and mesmers. Drop it at your feet while kiting and when they try to blink to you, they will port directly into the cc.
Harbinger’s “tradeoff” for its excellent damage, mobility, and CC is that it doesn’t have a second health bar like other necro specializations; this part of the class incorrectly led many necromancer mains to assume harbinger would have no sustain. However especially with death magic, harbinger is extremely difficult to kill.
Use your Well of Corruption to shut down boon heavy classes classes such as supports, catalysts and chronomancers. Focus on using it when they get access to Stability. Well of Darkness counters meele professions like Warrior, Willbender, or Elementalist very effectively.