The Ergon

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

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Omega created the Ergon with his power to create with the 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)