Speravore

Speravores were a squid-like species which fed off of potential. (AUDIO: A Life of Crime)

They were used by Golden Futures to feed off of the potential of their sleepers - as well as the Sixth Doctor - to produce energy for Project Elysium. (AUDIO: World Enough and Time)

They were defeated by River Song and the Sixth and Seventh Doctors. (AUDIO: The Eye of the Storm)