Haemovores

"I am the last. The last living creature on Earth. I watched my world dying with chemicals, and I could do nothing. My world is dead."

Haemovores were a possible future evolved state of humanity, from an Earth rotting in polluted slime. The last Haemovore – the Ancient One – was transported to 10th century Transylvania, by the ancient evil called Fenric, to follow the flask in which it had been trapped by the Doctor. The Ancient One followed Vikings who stole the flask to northern England, picking them off, one by one. As the Vikings were drained of blood to become Haemovores themselves, the flask was buried and cursed. In 1943, cryptographer Dr Judson decoded the Viking runes, releasing Fenric. It then summoned the Haemovore army, dormant for centuries under the sea, to trap the Doctor into one final game. He tasked the Ancient One with poisoning the Earth with a toxin. Convinced by the Doctor that this act would create the dying future Earth of the Haemovores, the Ancient One destroyed Fenric - preventing the Haemovore timeline from occurring.