Tunnel Wraith

Tunnel Wraiths lived in the tunnels of a devastated planet. They often attacked the train-cities as they passed through the tunnels. According to Emiliege, they latched onto the psyches of acute minds.

In reality, Tunnel Wraiths and the entire train-city were part of an illusion that Maya had created for the Fifth Doctor and Nyssa. (PROSE: Confabula)