El-Adrel IV entity
The El-Adrel IV entity was an extremely aggressive lifeform native to the planet El-Adrel IV, previously unknown to the Federation, but known to the Children of Tama. 

This fast moving creature was nearly invisible to the naked-eye, only occasionally appearing as a visible blur as it moved, often letting out a loud, vocalized roar. Though it only appeared when it attacked its prey, it became visible, revealing large claws and spikes along its head. On sensors, the entity appeared erratically as an electromagnetic disturbance, not unlike a variable induction field, as it produced quantitative amounts of energy.

In 2368, Starfleet Captain Jean-Luc Picard and Tamarian officer Dathon were transported to the surface of El-Adrel IV by the Tamarians to join together against the entity, in the hopes that doing so would establish communications between the two species. The Tamarian language was based upon metaphors in their history and so any outsiders would be unable to learn it without knowing the Tamarian history. By re-enacting the legendary story of  and Jalad against "the Beast" at  – Picard and Dathon against the El-Adrel IV lifeform - the two were able to successfully communicate with one another.

However, this came at a price; the El-Adrel entity struck a mortal blow to Dathon, though his death was not in vain as it opened up a new era of communication between the Tamarians and the Federation. ()

Background information 
The El-Adrel IV entity was portrayed by stunt actor Rex Pierson, who received no on-screen credit for his appearance.

The entity was described in the script notes as an "Alien Creature" or a "Humanoid Blur". Its appearance described initially as "a distortion in the air – kicking up dust and brush." In further describing its actions, the script first stated that it gave off a "tremendous animal roar", and that there was "an almost imperceptible ripple in the air, a low electrical Crackling Sound coming from it." When Picard attempted to retreat, the script described how the entity was "cutting off the path Picard would have taken – almost as if to demonstrate its prowess. There's clearly no way to out run it." When it becomes visible and attacks Picard, the script described that "It is a horrifying creature surrounded with a shimmering electrical field," and when he struck it "The dagger contacts the field (not flesh); the creature shrieks angrily in response."

To create the creature, the makeup department built a huge head, first by creating a mold out of two hundred pounds of plaster and then by casting it out of polyurethane in three separate pieces. Also built by the makeup department was the creature's hands, while the costume department created the body. In the monster segments, the creature was assembled using computer-generated optical effects that put the shots of the head, body and hands together and enabled the creature to move and twist its head. For the closeups, the head was mounted on a stand and fitted with a lever that opened and closed its mouth. (Star Trek: Aliens & Artifacts, p. 121)

The creature's unusual "glowing" was realized with a less expensive version of the -type melting effects. Going from tape to film and back again, the creature was shot against a blue screen on fast video and developed on film 10 stops over the exposure. The scenes featuring the El-Adrel lifeform were filmed on location at Bronson Canyon, in an area below the famous Hollywood sign, on  and , under the supervision of stunt coordinator Dennis Madalone. ()

The mask worn by Pierson was later sold off in the It's A Wrap! sale and auction on eBay.   One of the two props is now owned by RedLetterMedia. 
Unnamed species
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Non-corporeals