From Halopedia, the Halo wiki
The Promethean Soldier is a class of the armiger developed and primarily used by the Forerunner Prometheans. They are a commonly recurring enemy in Halo 5: Guardians, mostly replacing the Promethean Knights prominently featured across Halo 4.
Soldiers are mainly seen with Suppressors and LightRifles like the Knights in Halo 4, although they can also carry Scattershots, Binary Rifles, Splinter Turrets, or even Incineration Cannons. Soldier Snipers are most commonly armed with Binary Rifles, although they can also switch to Suppressors if a player gets close to them. Soldier Officers are most commonly armed with Splinter Turrets, although they also use Suppressors, LightRifles, Scattershots, or Incineration Cannons. Rarely, Soldiers are even seen using non-Forerunner weapons, like SAWs in the campaign mission Unconfirmed or UNSC and Covenant weapons in Warzone and Warzone Firefight.
Soldiers are capable of phasing, which involves them using slipspace translocation to quickly move around the battlefield to confuse and/or surprise their enemies. It is highly recommended for players to keep a phasing Soldier in their sights and find where the Soldiers phased to in order to engage them.
Soldiers feature breakable armor, much like Brutes, and are weak at their exposed joints. Before their main weakspots are exposed, one can shoot their chest or shoulders which break significantly faster when compared to the head. Once their armor is broken, their faces become exposed and they can then be killed with a single headshot using a precision weapon. Breaking their armor is possible with several precision weapon rounds, like 3~5 scoped-in LightRifle shots. The Boltshot is also effective against Soldiers. However, it is never a good idea to engage Soldiers while unshielded, especially on Heroic or Legendary, as the Soldiers will more often than not retaliate with a fatal blow from their weapons. In addition, the Plasma Pistol is totally ineffective against Soldiers, as they are completely impervious against the Noob Combo, even more so when compared to Brutes or Knights in Halo 4. In addition, Soldiers will occasionally perform random idle animations in the middle of combat, leaving them exposed to attack.
Just like Elites, Soldiers can hijack or board vehicles. In Warzone and the campaign, Soldiers piloting vehicles are commonly seen in Phaetons or Ghosts. Also, just like Elites, Soldiers have no qualms about changing their weapons depending on the range at which they engage their enemies; they are seen doing an animation where they hold their right arm in the air and spin it to change their weapon.
In Warzone and Warzone Firefight, there are Legendary and Mythic versions of the Soldier, each with significantly higher health and strength. The Legendary Soldier sports an orange color with teal highlights and uses heavier weapons like the Dying Star LightRifle as his armament, while the Mythic Soldier is colored maroon with bright red highlights and sometimes tends to use Rocket Pod Turrets as his weapon, making him even more dangerous. In addition, Legendary Soldier bosses also appear, driving stolen UNSC vehicles, such as Warthogs or Mantises.
Replacing the Crawler Snipe from Halo 4, the Soldier Sniper can be considered more dangerous than a Jackal Sniper due to the fact that he is most commonly armed with the Binary Rifle, which can instantly kill a campaign player character and make them unrevivable until their next respawn, especially on Heroic or Legendary, so long as most of the beam hits. For this reason, Soldier Snipers should be high-priority targets and eliminated as quickly as possible.
Despite this, Soldier Snipers are the least well armored of the three types of Soldiers, as they die to a single headshot from a precision weapon, regardless of difficulty setting, in the same manner as Crawlers, Grunts, and Jackals.
Getting too close to Soldier Sniper usually incites them to drop their Binary Rifles or LightRifles for a Suppressor, so it is highly recommended to kill the Soldier Snipers from a safe distance or as quickly as possible in order to retrieve their weapon or grab ammo from it. When the player is spotted, looked at, and targeted by a Soldier Sniper, they receive a red glare on their screen and heads-up display as a warning.
In the campaign, the Soldier Sniper appears in the following missions:
The Soldier Officer, also known as the Soldier Captain, is a more heavily armed and armored type of Soldier who speaks in a drastically different robotic voice from his lesser counterparts and is commonly armed with either a Scattershot, LightRifle, or a Splinter Turret. He most often leads lesser Soldiers.
It is highly recommended to deal with him from a safe distance as the Splinter Turret's projectiles are dangerous due to their strong knockback that can easily disrupt a Spartan while they are reviving another Spartan, which can then lead to the entire fireteam dying quickly. Use the scenery and thruster pack boosting to evade the projectiles, seek cover, and then fire away at the Soldier Officer with a precision weapon and/or explosive weapons.
In Warzone and Warzone Firefight, Legendary and Mythic Soldier Officers appear, armed with heavier weapons like Rocket Pod Turrets. They can survive multiple hits from heavy vehicle weapons like a Banshee's fuel rod cannons before dying.
All campaign missions that feature enemy Soldiers have Soldier Officers as enemies except for Osiris, although there are normal Soldiers wielding Splinter Turrets in that mission.