Chi Beasts (Also known as Eaters of Life or The Dark Ones.) are a group of humans or any other species that have lost any trace of chi in their bodies, essentially they are wild animals that will consume the chi of anything living. They are considered extremely dangerous. While Chi Beasts did not appear in the main TMNT timeline, they are central antagonists in the spinoff; TMNT X-treme. Chi Beasts are sentient beings without chi. Their hunger stemming from their own lack of said substance.
Chi Beasts are created from any form of intelligent life that have experienced extreme emotional trauma. The transformation itself is heralded by symptoms of extreme clinical depression; random bouts of violent rage; night terrors (severe nightmares that the victim cannot wake up from); and the occasional vomiting of a black ink like substance.
The actual transformation itself involves black tendrils expelling from the victim's mouth that tightly wrap them up. They may remain in this state for minutes, days, or even years. Eventually they burst forth as a fully transformed (Albeit low level) Chi Beast.
A Chi Beast's strength is determined by the amount of chi they have recently consumed. Like human food, a certain amount of chi is required for the Chi Beast to run its body, but consuming such a low amount would leave them extremely weak. Normally a Chi Beast will constantly seek out living humans to drain of chi, thus giving them a certain amount of power.
Chi Beasts will change form after reaching a certain level of power. At which time they take on a new form and greater powers. The levels of a Chi Beast in order are:
Stalkers are the lowest level of Chi Beast evolution. They generally appear as large (10 ft. tall) vaguely animal shaped creatures that generally carry themselves like a large ape. However, their size belies unprecedented speed and agility. Also closer inspection of their bodies reveals that they are composed of a substance akin to black slime. All Stalkers possess vaguely human skull shaped heads with three slit eyes. An interesting feature is that some stalkers possess special appendages or features that prove beneficial in combat or luring in prey. Examples of this are Fisher Tiger's lure, and Daz Bone's back spines. One of a Stalker's most infamous features is that they are invisible to any form of non eye using methods of observation (Such as Kon's spirit sense or modern day sonar). All Stalkers are little more than animals, never practicing any form of subtlety or restraint.
After a Beast has a large enough store of unused chi, they will undergo a second transformation. They become slightly more humanlike, while gaining something akin to armor on their bodies, their size also decreases to around seven feet tall. In this form, their total conserved chi is compresses into this smaller body. This gives them explosive speed and interestingly some semblance of intelligence. Their skin also hardens to the strength of soft metal, while they retain their skull shaped head. They lose all trace of their old animalistic tendencies, along with their recklessness. In exchange, they become calmer and more focused, but are still obsessed with consuming as much chi as possible and are still utterly ruthless hunters. Their obsession is not unfounded, because if a Beast does not possess any chi in its body even for a moment, they will revert back to stalkers and lose any ability to evolve again.
A newly transformed Beast.
Ghouls are the third level of Chi Beast evolution. They appear as animated black cloaks with white masks. Unlike the first two forms, ghouls are completely silent. The only sound they ever make is a low airy rasp used to communicate. In this form, they possess high levels of tactical knowledge, and are extremely cunning. Also Ghouls have been shown to produce small amounts of "Anti-Chi" that they can shape into a sword or other weapon. The color of this "Anti-Chi" is usually the color opposite of their chi before their transformation. For example, a person who possessed blue chi would have red "Anti-Chi".
A Ghoul level Chi Beast.
Lord is the fourth and final level of a Chi Beast's transformation. A lord level chi beast appears fully human, the only non-human trait being their red eyes. Like Ghouls they produce "Anti-Chi" as well. Unlike ghouls, they produce and hold massive amounts of the substance. The final transformation heralds the most extreme changes; all Chi Beasts at this level lose their hunger for chi completely, they are capable of using "Anti-Chi" to nullify chi based techniques, or create new techniques unique to them. While Lord Chi Beasts possess human level intelligence, they are rather unfriendly and aloof as a species. Despite this, they will always keep their word (though it is near impossible to gain it in the first place) and are fiercely loyal to anyone who gains their respect. As such, a Lord would be last to take your side, and the last to leave it. Lords are also massively powerful shown when Allen, then a freshly evolved lord fought the entire Ninja Tribunal and their acolytes to a standstill.
Lords also possess some form of weapon, normally a katana that they carry with them at all times. It is revealed by Allen that these weapons are the compressed physical form of the Lord's bloodlust. All Lords are capable of "releasing" their blade; turning them into a combination of their old animal self and their current form, called an Orexis. In this form they possess the wild instincts of their old forms, along with explosively enhanced powers. All Orexi are unique, none are similar in any way.
A rare gathering of Lords.
Allen's appearance as a Lord Chi Beast.
A Lord Chi Beast demonstrating Anti-Chi
A Lord Chi Beast in Orexis.