Eitr
From Tomb Raider Wiki
In Norse Mythology, Eitr was a substance which had life-giving properties, but also ironically was a strong poison, or a venom, from the Midgard Serpent, or Jormungandr.
Thor, on the last battle - Ranrorok, was said to have killed Jormungandr, taken ten steps but then to have succumbed to the poison, and died.
In Tomb Raider: Underworld
Eitr is a substance that Lara Croft comes across various times in Tomb Raider Underworld. It is a bright blue liquid that causes instant death and re-animation to anything that falls into it.
It is encountered in Xibalba and in the Arctic Sea. It was responsible for the death and re-animation of Tigers, Yeti, many unknowing Mayan tribesman and Vikings, the Doppelganger and Amelia Croft. They are now known as Thralls.
