G is for... Gellguards

Servants of Omega, the Gallifreyan stellar engineer who had supposedly been killed supplying his people with the power they needed to begin their time travel experiments. He had instead been blasted into the universe of anti-matter, where he remained trapped for millennia. The Gellguards were created by his willpower from raw anti-matter, in a process called psychosynthesis. Omega realised that the only way he could escape his captivity was to find another Time Lord who could take his place and maintain the domain he had created. He began draining the energy of the Time Lords and then sent a gell-creature to Earth to seek out the Doctor. This creature could survive in both universes, and was designed to transport the Doctor into Omega's realm. When it failed, Omega sent more gel creatures to attack UNIT HQ, forcing the Doctor to take refuge in the TARDIS. He was joined there by his earlier incarnation - sent by the Time Lords to assist him. Blobby, one eyed, creatures, the Gellguards had a single limb which could fire powerful energy bolts. Once the Doctor and Jo had been transported through a Black Hole to the universe of anti-matter, Gellguards were sent to capture them. They later captured the Second Doctor and Sergeant Benton, after UNIT HQ had been transported through the Black Hole.
As they were creations of Omega's mind, they would have ceased to exist once his domain was destroyed.
A later attempt at psychosynthesis by Omega resulted in the Ergon creature.

Appearances: The Three Doctors (1972 / 73).

• The naming of these creatures varies. I have gone for the most common version, but you could also have Gell Guards, Gel Guards or Gelguards.