Gell guard

Gell guards, also known as Gel Guards (PROSE: Interference - Book One), were blob-like creatures that Omega created while trapped in a black hole domain made of anti-matter.

Biology
They had the ability to travel from Omega's anti-matter universe into that of matter. They were unaffected by gunfire and explosions and could use their claws as weapons to create explosions of their own. (TV: The Three Doctors)

History
Following many of Omega's first creations escaping the anti-matter universe with the Second Malika, an enraged Omega murdered his remaining creations and heated their flesh into a burning primordial soup from which a more simple servant to his power could be born, the first Gel Guard. (COMIC: Omega)

Under Omega's command they attacked UNIT HQ. They killed a number of soldiers, captured the Third Doctor and his friends, and took them to Omega. (TV: The Three Doctors)

Other references
The Gel Guards were one of the species referenced in UNISYC's Theoretical Monsters: A Credibility Test. (PROSE: Interference - Book One)

Behind the scenes

 * The name "Gell guard" is never used on-screen. It first appears in the Doctor Who universe in Interference - Book One.