Halo Wars 2

This achievement is earned during Mission 4, "The Archive."

After being introduced to Voridus' Infusion gel, the game will prompt you to use the Brute's special ability to clear out a large wave of Flood. Following this, as you enter the next area, you will have a forced interaction with a Forerunner teleporter. These teleporters can be used to call in reinforcements (simply stand near the base plate and press , then choose which type of unit you want). For the purposes of this achievement, you must ignore calling in any reinforcements until you reach the final chamber of the facility.

This is best done while playing on Easy since the only units you begin the mission with are Voridus, three Jump Pack Brute units (2 Brutes per unit), and three Elite Rangera units (2 Elites per unit). By mixing these units' abilities/tactics with the various Leader powers - such as Infusion Wake and Cataclysm - you should have very little trouble making it through the mission with such a small army. Don't be mistaken, though: towards the end of the mission, you may lose your Jump Pack Brutes and Elite Rangers and be left only with Voridus. Just make sure to utilize Atriox's Bulwark often in order to heal your squadron before moving onto the next fight.

Once you reach the final chamber of the facility - the room that has the Flood-covered locks - the achievement will unlock. It's also at this point in which you can finally call in reinforcements to help supplement your firepower during the final assault.