Sea creature (Thin Ice)

A creature which resembled a giant fish was imprisoned under the River Thames until 1814. (TV: Thin Ice)

Biology
The creature was massive in size, easily several times that of a whale. It shared many similarities with lure fish, namely the overall shape of its body, its fins and its bioluminescent lure on its forehead. The creature was female and could produce several offspring who were the size of regular lure fish.

The creature's race were extremely long-lived and could potentially live for centuries, perhaps even millennia.

The Twelfth Doctor affirmed they were of terrestrial origin, perhaps from Earth's prehistoric era like the Silurians and the Sea Devils. (TV: Thin Ice)

Diet
The creatures were carnivorous and fed on meat, mostly humans. (TV: Thin Ice)

Abilities
The creature's presence alone seemed to cause intensely cold temperatures, enough to freeze the whole River Thames solid in winter.

The creature's feces made for an ideal fossil fuel. It could burn slower and longer than coal, and could even burn underwater. (TV: Thin Ice)

Behaviour
Neither the Doctor nor Bill knew what would happen when the creature was freed. Instead of lashing out at her captors, the creature, once freed, swam away to the ocean. Despite her colossal size, she was careful not to harm anyone or collide with the bridges and buildings lining the river at South Bank. (TV: Thin Ice)