Halo Wars 2

This achievement will unlock once all five missions of the Campaign have been successfully completed on either a Solo or Co-Op Legendary playthrough (mission select is fine, too). Like the main Campaign, the Legendary difficulty will increase the AI's health and damage output. Moreover, the AI will play much more aggressively. Again, as suggested for the main Campaign, one of the best tactics when playing on Legendary is to rely on a strong defense; fortifying bases with Turrets is key and Aerial Units are an extremely efficient to build (when possible), as are Engineers.

If you have collected the various player-strengthening Skulls prior to playing a mission on Legendary, feel free to activate them in the pre-mission lobby (available via Mission Select) as to make things easier for yourself. The best Skulls to use on a Legendary playthrough are:

• Pain Train
• Bountiful Harvest
• Emperor
• Total Annihilation
• Firestarter
• Things That Go Boom
• Sugar Cookies

The ability to use the Skulls listed above should be a significant help in making an otherwise difficult feat more manageable. Make sure you are utilizing the manual save function as often as possible, too; when you get past a tricky section of a mission, make a save as to avoid having to replay some of the mission if things go wrong.

For additional guidance in completing each mission, please refer below for some key tips.

Overall Tips

• Build Engineers. They will help keep your defenses and units alive. The Flood will rarely attack Engineers, which makes them great as both mobile and stationary healing beacons.
• Prioritize Aerial and Vehicular Units over standard Infantry Units (Grunts, Brutes, Elites, and Hunters).

Mission 1

• Focus on keeping the Locusts alive, as you cannot build additional Locusts in this mission.
• Do not feel compelled to capture every single mini-base, though do take time to build and upgrade as many Turrets as possible while moving through the mission.
• Focus on building up an army of Banshees and Engineers in this mission to supplement the Scarab's attack power and help keep it alive and well.

Mission 2

• Keep your Goliaths alive! It's recommended to make sure there is at least one Engineer per Goliath duo (during the second line of defense).
• Once you reach the final line of defense, move quickly to get all three Blisterpacks online. Once operational, leave one or two Engineers with each Blisterpack and build/upgrade a Turret near them, too.
• Ignore the Energy Nodes during the final line of defense; you will likely get overwhelmed with your forces that far away from the main HQ.
• During the final line of defense, you should focus on building up an army of Engineers, Banshees, and Wraiths. The Banshees and Engineers can cover the north, while the Wraiths and Pavium can cover the south.

Mission 3

• Do not bother capturing all four Flood-infested mini-bases. It may only be wise to capture a single one for a small increase in Supply production.
• Build a Mega Turret at your main HQ when you enough Energy and then build the Lingering Damage upgrade.
• Focus on building an army of Banshees, Engineers, and, if you desire, Blisterpacks.
• Do not stay out in the field for too long when the pressure begins builds up. Once the pressure builds up to 70%+, fall back to your main HQ.
• Towards the end of the mission, when the Abominations join the fray, use "Stasis" to slow them down (if there are more than one).
• Engineers can repair the drill, so use them wisely during the final defense.

Mission 4

• Use Infused Gel often to lay waste to the lesser Flood Infection forms, but avoid combat when you can.
• The supply caches off the main path should be collected, but don't wait around to destroy the Flood Tentacles.
• At the malfunctioning light bridge, it's okay to sacrifice any Elite Ranger Units you may have. Focus on controlling Voridus, using his Infused Gel and Cataclysm to destroy the Flood when you can.
• Don't be afraid to use Voridus to rush through the laser defense systems. His shields and high HP means he can tank damage pretty well.
• In the final chamber, focus on keeping only two locks intact. Don't hesitate to run circles around the perimeter of the chamber, if needed.

Mission 5

• Focus on building an army of Engineers and Banshees.
• At Mega Turret sites, leave on stationed Blisterpacks and one Engineer back; this will keep the Turrets safe from potential Flood attacks.
• After constructing the first Mega Turret, hang back at your main HQ and build/upgrade your units. So long as you hang back and avoid encountering the Proto-Gravemind, you have all the time in the world to amass your army.

Once all the five missions have been completed on the Legendary difficulty setting, this achievement will be yours.