The Ergon

The Ergon was a reptilian/avian creature created and used by Omega as one of his agents in the universe of matter.

Biography
Omega created the Ergon with his power of psychosynthesis. He considered it one of his less successful creations. (DW: Arc of Infinity) Bizarrely, while on Earth (presumably in Perivale, where she grew up), Ace saw him while working at a fast food restaurant. Ace at the time mistook it for a person wearing a costume. (DWM: Anti-Matter with Fries)

It used an Anti-Matter converter with which he shot Colin Frazer, Tegan Jovanka and Robin Stuart to assist Omega. While wrestling with the Doctor, Nyssa took his gun and shot him. (DW: Arc of Infinity)