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 levels higher than the level average for the mission, and some have resistances to more damage types, 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.

As of Update 13, 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. They are not noticeably more durable or dangerous than their base type, aside from any benefits gained from increased level such as increased health and armour.

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

Before U13, Blitz Eximus units used the prefix "Blast".

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

Drains energy from nearby enemies within 15 meters at the rate of 5/s.

Energy Leeches can be seen on close combat units such as Corpus Prod Crewmen and Grineer Butchers. Infested Energy Leech Eximus units are called Parasitic Eximus, and are extremely common among all types of Infested.

Arson/Caustic
"Heat based attacks and auras"

Arson Eximus units have the ability to create a Fire Blast similar to the one used by General Sargas Ruk, knocking down any enemies who are caught in the blast.

Unlike the Grineer, who use the prefix "Arson", the Infested have Caustic Elders; these behave largely the same, and are capable of releasing a Fire Blast. Arson Eximus units are nonexistent for the Corpus.

Before Update 13, Arson Eximus units had the prefix "Fire".

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-restoring pulses, similar to the healing wave effect of Ancient Healers, but with a blue grid-like pulse rather a green wave.

Guardian Eximus units are exclusive to the Corpus, which should be of little surprise given their fairly extensive use of shields, though Corrupted Crewmen can also manifest as these. Eximus units of this type are usually MOAs and Ospreys.

Arctic
"Cold based attacks and auras."

Arctic Eximus units can generate a temporary Snow Globe-esque barrier to protect themselves and allies. Their version follows them when they move as opposed to being stationary like the conventional Snow Globe power, and has a unique and distinctive Truncated Icosahedron design to it. They have additional ice-based attacks as well.

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, leaving them (and any of their allies within) vulnerable. The globe also dissolves by itself after a certain amount of time, so hiding in cover and waiting for the globe to dissipate is an alternative tactic.

This Eximus type is very common amongst the Grineer and Corpus.

Before Update 13, Arctic Eximus units used the prefix "Ice".

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

The prefix and subtitle for this Eximus type are slightly misleading; these enemies do not seem to steal the target's health per se. Instead, they regenerate health by inflicting damage. This is easily observed after damaging them as they will regain health from damaging a target's shields, or a target that has Iron Skin active.

Leech Eximus units are common in Grineer ranks, but are nonexistent in the Corpus. Infested Eximus units use "Sanguine" in place of Leech, but otherwise behave identically. This should not be mistaken for the Energy Leech prefix noted above.

Before Update 13, Leech Eximus units used the prefix "Lifesteal". Sanguine remained Infested exclusive.

Shock
"Electric based attacks and auras."

One of the most dangerous types of Eximus units, Shock Eximus units emit a status effect aura that affects all enemies within a 5 meter radius. The screen will also distort in a similar way to the effect of an Ancient Disrupter's attack. 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, typically appearing on Elite Crewmen or Corpus Techs.

Before U13, Shock Eximus units used the prefix "Mag".

Venomous
"Toxin based attacks and auras."

Eximus units that exhibit this trait are capable of delivering attacks towards their adversaries and also have the ability to emit a more potent aura of toxins to their surroundings in a larger area than those of regular Toxic Ancients. When inflicted, an 8 second Toxin 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.

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, potentially receiving massive, if not fatal damage.

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  damage.