Eximus

Eximus units (previously referred to as Leader units until Update 13)  are special 'elite' variants of standard enemies introduced in Update 12 that can appear in any mission type. They come with special abilities, some of which are similar to Tenno and are sometimes much stronger than an average member of their faction, though effects vary from type to type. Eximus spawn 10-15 ranks higher than the rank average for the mission along with the highest increase in stats and resistances, posing a reasonable challenge for under-equipped or inexperienced Tenno.

Almost any base unit type (Osprey, Lancer, MOA, etc.) can spawn as an Eximus, though certain units can only spawn as a particular Eximus type, e.g. Chargers can only spawn as Parasitic Types. They can easily be identified by their special auras and larger sizes, and frequently have unique textures/skins to make them more visually distinctive.

All Eximus units were given their own Codex log, essentially doubling the Codex library. Some factions may have only a certain type of Eximus that the others do not have, such as how Shock and Blitz Eximus are exclusive to Corpus units. Additionally, all Eximus-type units have a chance to drop components for the Oberon Warframe when defeated.

Upon death, Eximus units provide four times the regular affinity gain of their regular counterparts, added after their level differences.

Blitz
"Defends itself with a radial Blast Attack."

Blitz Eximus units are capable of casting Seismic Shockwave, which knocks down nearby opponents. Eximi of this type has an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

Blitz Eximus are exclusive to the Corpus, mainly appearing on all models of MOAs and some Crewmen.

Energy Leech / Parasitic
"A tank who drains Energy from nearby enemies."

Energy Leeches/Parasitics units are capable of draining players' energy within 15 meters at the rate of 5s-1 (non-stackable effect). These eximi are commonly a close combat units such as Corpus Prod Crewmen and Grineer Butchers, as well as the Corrupted versions of the latter. Infested Energy Leech Eximus units uses the prefix Parasitic Eximus, and are extremely common among all types of Infested. Eximi of this type have 300% of their base health and shield and an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

Arson / Caustic
"Heat based attacks and auras"

Arson/Caustic Eximus units projects a fire resistance aura their allies nearby, which nullifies all damage, this aura also extends to combined damage and will nullify the  damage of said combined type. They have the ability to release a Fire Blast similar to the one used by Ember, damaging and knocking down any enemies who are caught in the blast. The knockdown can be negated by blocking with a melee weapon. Eximi of this type has an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

These Eximus units will release their fire wave when enemies are close to them, and are capable of dealing significant damage to Sentinels at higher levels; caution is advised when engaging them at close range.

The Infested uses the prefix Caustic Elders instead of Arson; these behave largely the same, and are capable of releasing a Fire Blast. This Eximus variety is common among Grineer, including Corrupted versions, but the Corpus do not field any kind of Arson Eximus.

Guardian
"Restores shields of nearby allies."

Guardian Eximus units are especially durable, gaining a significant boost to their own shield durability as well as the mentioned shield-restoration effect. They release radial shield charge in a blue-grid restorative pulse. Eximi of this type has an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

Guardian Eximus units are exclusive to the Corpus (and their corresponding Corrupted counterparts), which should be of little surprise given their fairly extensive use of shields. Eximus units of this type are usually MOAs, Orokin Drones, and Ospreys.

Bug:

Eximus units' damage resistance has its capped around 75%, however, Update 18 introduced a bug that Guardian Eximi with Proto Shields are completely immune to ,  and damage.

Arctic
"Cold based attacks and auras."

Arctic Eximus units projects a cold resistance aura their allies nearby, which nullifies all damage, this aura also extends to combined damage and will nullify the  damage of said combined type. They can generate a temporary Snow Globe barrier to protect themselves and allies. Their version follows them when they move as opposed to being stationary like Frost's, and has a unique and distinctive Truncated Icosahedron design to it. They have additional ice-based attacks as well. Eximi of this type has an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

Arctic Eximus units are among the most dangerous variety, as their ice slowdown aura is fairly large, whilst their snowglobe protects them from ranged attacks. Certain targeted powers, like Oberon's Smite and Volt's Shock, can damage the target through the snowglobe. Like the regular Snow Globe, inflicting enough damage will cause the Arctic Eximus' Snow Globe to disintegrate. Note however that the globe had object-based health and is not affected by crit damage, rendering crit-focused weapon to be less effective than raw damage weapons. The globe also dissolves by itself after a certain amount of time, therefore hiding in cover and waiting for the globe to dissipate is an alternative tactic.

This unit variant is reasonably common amongst the Grineer and Corpus (including Corrupted versions of both), but nonexistent among the Infested.

It is possible for Grineer Napalms and Scorches to spawn as Arctic Eximi. If the player suffers a fire proc while within the Eximi's aura, the fire proc changes to a Blast proc (possibly a bug, imperfect chance of happening).

Leech / Sanguine
"Life leech weapon, enhanced health."

Leeches and Sanguines regenerate health by inflicting damage. This is easily observed after damaging them as they will regain health from damaging a target's shields/health, or a target that has Iron Skin active. Eximi of this type have 300% of their base health and shield.

Leech Eximus units are common in Grineer ranks, but are nonexistent in the Corpus. Corrupted Eximi can also spawn in this variant. Infested Eximus units use the Sanguine prefix instead of Leech, but otherwise behave identically. This should not be mistaken for the Energy Leech prefix noted above.

Shock
"Electric based attacks and auras."

Shock Eximus units projects an electric resistance aura their allies nearby, which nullifies all damage, this aura also extends to combined damage and will nullify the  damage of said combined type. They also emit a status effect aura that affects all enemies within a 5 meter radius. The effect is constant until the Eximus is defeated or until the Tenno moves out of range. Shock Eximus units are exclusive to the Corpus (and Corrupted Crewmen), typically appearing on Elite Crewmen or Corpus Techs. Eximi of this type has an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

Venomous
"Toxin based attacks and auras."

Venomous Eximus units projects a toxin resistance aura their allies nearby, which nullifies all damage, this aura also extends to combined damage and will nullify the  damage of said combined type. They are capable of delivering attacks towards their adversaries and also have the ability to emit a potent aura of toxins to their surroundings in a 10 meter range. When inflicted, an 8 second proc will persist and deal moderate damage over time, depending on the level of the enemy which inflicted the proc. Venomous Eximus units are exclusive to Infested Ancients. Eximi of this type has an innate resistance of 50% to all damage types, added additively from all three of their health type, shield type and armor type.

Synthesis Target
Classified as an eximus, a Synthesis target is a marked target for Cephalon Simaris. Synthesis targets have far more health than their regular counterparts (preventing players from killing them accidentally, though it is possible for players to kill them regardless), and have at least 3 nodes visible through the Synthesis Scanner. Scanning at least one node will cause the Synthesis target to run away from the player and gain a random special ability to evade capture, like leaving a trail of clouds.

Prosecutors
A unique variant of Eximus units exclusively for the Grineer Guardsmen on Ceres, that provides near invulnerability on itself and to its allies while remaining vulnerable to a single primary elemental damage type. Eximus types vary between Shock, Fire, Ice, and Toxic.

Warden
"Life Leech weapon, increased speed, weak to stealth attacks."

A special Eximus variant of the Wardens introduced in Rescue 2.0 missions, featuring Life Leech and enhanced movement speed. However, they are extremely vulnerable to stealth attacks, and will most likely receive fatal damage from it.

Sensor Regulator
A unique Eximus variant of the Sensor Regulator that was introduced circa Update 18. These Sensor Regulators have 100% additional armor, and 200% additional health, making them far more durable than a normal Sensor Regulator. These Regulators are more likely to spawn in Sorties.

Trivia

 * Before Update 13, most Eximi had different prefixes; Blitz used to be called Blast; Arson used to be called Fire; Arctic used to be called Ice; Leech used to be called Lifesteal; and Shock used to to be called Mag.
 * Up until Update 13, The Sergeant could spawn as an Eximus, quadrupling his affinity and greatly increasing his health.
 * According to Digital Extremes, Eximi are the result of the following;
 * Corpus Eximi Crewmen are members of the elite who are bestowed specially-designed suits, whereas MOA and Osprey Eximi are produced on a regular basis.
 * Grineer (barring Rollers) and Infested Eximi are the products of genetic mutation, though in the case of the Infested, the genes that contain said mutations are present in the DNA of all known Infested, suggesting that some form of gene expression regulation is in effect.
 * Although no explanation was given for Roller Eximus, it's likely they are produced much like MOA and Osprey Eximi.
 * Corrupted Eximi are simply corrupted versions of the above units.

Bugs

 * Beginning with the Cold Revenge Tactical Alert, the Shock Eximus' aura does not function properly, allowing players to get close to it without suffering  procs.
 * Some Eximus units require the same amount of Codex scans as their original variant to complete their entry, as opposed to only requiring three Codex scans. This usually occurs when new enemies are put into the game and is usually fixed shortly afterward.
 * Eximus units' damage resistance has its capped around 75%, however, Update 18 introduced a bug that Guardian Eximi with Proto Shields are completely immune to ,  and damage.