Unknown Entity

The Unknown Entity ('Fluffy', as it is half-jokingly known by some Tomb Raider fans) is the creature Amanda Evert commands throughout Tomb Raider Legend using a pendant she and Lara discovered in Peru. The Unknown Entity devours or kills many of Lara's colleagues at a dig site, where Amanda was thought to have died. During the boss level at the end of the game, Amanda combines with the Unknown Entity to create a powerful foe which can only be defeated using the Excalibur. The Unknown Entity is the final boss in Kazakhstan and Bolivia Redux. In the laboratory of the Russians in Kazakhstan, Lara can't fight against it. She has to run and activate the Tesla tower by pulling switches. If she has activated the tower, Lara can use the magnetic machine to ban the Unknown Entity for a while. In the Level Bolivia Redux Lara uses Excalibur to kill the Unknown Entity.

'Fluffy' was most likely left in the tomb to protect the Queen of Tiwanaku from people trying to enter her burial chamber.

Although the Unknown Entity was killed at the end of Tomb Raider Legend, Amanda seems to wield similar powers in Tomb Raider Underworld, with the same red/orange glow.