Psimorph

Psimorph is an extradimensional alien capable of using psionic powers. They're from 1997 game X-Com: Apocalypse.

Overview
Despite an appearance that somehow resembles a creature with legs and arms, a psimorph is actually a massive, jelly-like alien that needs internal implants and devices to keep it from collapsing into a puddle. It's form has multiple small tentacles at the far end of it's four protrusions easily mistaken for limbs.

Inside of a psimorph reveals a mass of vital organs without any kind of supporting structure - skeleton or any other. Internal devices that create antigravity field are also the reason why it's twelve separate brains won't squish each other into messy goo.

Psimorphs don't wield any conventional weapons. They rely solely on their devastating psionic abilities. This is also a weakness; fully mechanized troops can take psimorphs down with ease as long as their bodyguards have been neutralized. However, being high-ranking alien, psimorphs are often accompanied by such powerful creatures as Megaspawns or heavily armed Skeletoids.

Role in invasion
A floating mass of multiple brains makes for a fine commander, and such is the role when Psimorphs are encountered in our dimension. They're most often leading bigger alien UFO's such as the mothership. While their presence is an enormous threat, they are rarely in the forefront of an assault.

In the alien dimension they are far more numerous in the alien buildings. There they are most likely overseers.