Halo Wars 2

This achievement can be done in a Solo Firefight match or an online game with other players, although it's easiest when playing with 1-2 other players.

While playing Terminus Firefight, you should notice several plots of land around the map: long, rectangular plots around the perimeter of the map for Barricades, and medium-sized square-shaped plots around the perimeter of the map for mini-bases. Once you have a steady flow of resources coming in from your Supply Pads and Generators, as well as a sizable army to defend the Terminus, begin coordinating with your teammates to move around the map in an effort to build.

You can choose to tackle these achievements in one of two ways, though the second method may prove to be more efficient:

1. Have your teammate(s) use their army to defend the Terminus while you set off with your own medium-sized, mixed squad of Aerial, Infantry, and Vehicular Units. Move around the entirety of the map, stopping at each Barricade plot and mini-base plot to build. While building, stay put to see construction through, and then reinforce the Barricades/bases with upgrades.
2. Each player should focus on expanding their "territory" around the map with their own armies and resources, making sure to leave at least half of their Units at the Terminus in case the enemy pushes through fortified lines.

Once every mini-base plot has been built upon at the same time, "Outflood the Flood" will unlock. Conversely, once every Barricade plot has been built upon at the same time, "Walled In" will unlock.