Raise an Army for Skyhold

If your Warrior has completed Argus questing, purchase Krokul Ridgestalkers from an NPC in Krokuun and Void-Purged Krokul from an NPC in Eredath, and Lightforged Bulwark from an NPC in the Vindicaar for 150 Order Resources each ( 900 Order Resources for additional purchases per week). Each troop type is Unique (5), meaning you can hold a maximum of 5 at a time, so you can recruit up to 7 of each type before the cap forces you to let some die first.

Troops cannot be manually dismissed, so send them on missions with the Lethal hazard (green skull) without countering it, which reduces their vitality to zero and removes them, freeing up slots to recruit replacements. The Argus troops have no 30-minute wait timer between recruits, allowing you to cycle through them faster than standard recruits and finish the achievement in approximately 5–6 logins by keeping up to 7 troops dying at once.

Recruiting troops from the Battle for Azeroth mission table also counts toward the 20-troop total, but the same rule applies: you cannot recruit new troops while any are still active, so you must kill them off via Lethal hazard missions before recruiting again.

This achievement is warbound, meaning every troop recruited on any of your Warriors on the same account contributes to the shared count of 20, so you can spread recruiting across multiple Warrior characters.