Infested

The Infested are what appear to be Corpus and Grineer Humanoids who have been taken over by the "Technocyte" plague. The majority of Infested seem to be former Corpus Crewmen or Grineer Lancers. However they are also speculated to also be partially made of consumed Tenno, hinted at by J3-Golem asking the Tenno, "Why do you destroy us, we are your flesh". This could explain the various powers or abilities some infested have. Most Infested do not have any significant ranged combat ability.

Walkers
The standard Infested unit. Runners and leapers appear to be bodies of Corpus humanoids, with various alterations and looks. They appear to have a fleshy "hand" perhaps made of infested tissue that is latched to their heads, suggesting the infestation may use this "limb" as a means to control the host during infestation. Their main purpose is to rush the players and overwhelm them with sheer numbers and brute force. It is possible to shoot limbs off humanoid walkers, such as forcing them to crawl by shooting off their legs. Their heads may also explode from headshots without killing them.

Crawlers
Infested walkers without legs. Very slow and relatively harmless, they can only crawl towards their targets. However, they tend to blend in with corpses and may succeed in an ambush. Crawlers cannot be knocked down and, as with other fallen enemies, are very hard to hit with most melee attacks. Using a finishing move is most effective against one.

Ancients
Ancients are large Infested that are much sturdier than standard Walkers. They have a large amount of health and will charge at players when close enough. Unlike walkers, Ancients can extend their arms to attack, vastly increasing their range. Ancients also come with special abilities, making them a nuisance on their lonesome, and a nightmare in groups. Their weak point is their feet and shins.

Although having the same general appearance as Corpus walkers, they are much larger in size, perhaps suggesting (along with their name) they have grown to their sizes by consuming an abundance of other life forms and may have been the first to be consumed by the plague or created, like J3-Golem.

Phorid
Phorid is the final boss of Eris, inhabiting Naeglar. Resembling an oversized and overbuffed Infested Charger, it bears a possibility of dropping blueprints for the Nyx Warframe and Neurodes resources.

J3-Golem
J3-Golem is the final boss of the planet Jupiter. He can be found on Themisto. He has a possibility of dropping one of the following on death: Volt Helmet, Volt Chassis and Volt Systems blueprints and Neural Sensors. He has also been known to drop 2x mods. He is thought to be the oldest boss, dating back to the Orokin Era.