Unknown Entity

Force Monster that Amanda Evert controlled came from The Wraith Stone in Peru. Whenever Amanda uses this stone she becomes one with the terrifying entity, then she uses this power to attack her foes. She only uses this power once, when Lara kills James Rutland in the Bolivia Redux level and Amanda was furious so she decided to finish this once and for all. When Amanda is defeated she loses The Wraith Stone.

Tomb Raider: Legend
During an expedition in Peru, the creature was awoken by a team of archeologists, including a young Lara Croft and Amanda Evert. The dig started off playfully enough, with Amanda teasing Lara about falling behind. However the screams of their companions of the creature caused them to cease their playful excursion, just before witnessing the creature slaughter some of their friends.

Lara and Amanda managed to escape the massacre as the site collapsed. Trapped in a large room, Amanda spied the Wraith Stone. With no other alternatives, Amanda pried the stone from the wall, hoping it could help. The creature then vanished, but the removal of the stone caused the room begin to flood, and a cave-in to occur. With Amanda's foot trapped underneath falling rocks, and water quickly rising, Lara was forced to leave, only after witnessing her friend's apparent death from said rocks.

However, Amanda survived, thanks to the help of the creature, which obeyed her as a result of her taking the Wraith Stone. From that day, Amanda could summon and even merge with Force Monster at will, simply by wielding the stone which she wore as an amulet necklace. Using the creature for her own selfish endeavors, she trained it to attack anyone who opposed her.

Amanda summoned the creature to retrieve the shard of Excalibur from a facility in Kazakhstan, warning Lara to stay out of it's way. Lara was able to fend it off with the help of a giant electromagnetic Tesla cannon, and retrieve the shard. Amanda called the creature back and escaped.

Amanda returned to the Dais in Bolivia to await Lara, knowing she would have the reforged Excalibur, which would act as a key to activate the Dais. Lara however wouldn't part with the sword and slaughtered Rutland and his men. Enraged, Amanda merged with the beast, in order to kill Lara. However Lara was able to finally kill the beast with the help of Excalibur. Lara then took the wraith stone from Amanda and locked it inside her vault.

Abilities
Force Monster appeared to evolve as it aged, growing larger in size and gaining the ability to fly, as apposed to running around on it’s arm like appendages. As well as it’s razor sharp claws, it also gained the ability to shoot projectiles of harmful energy. When under Amanda’s control, she can use The Wraith Stone to heal its wounds.

Appearance
Force Monster resembles a demonic creature with no legs, two large arms with long claws, and a skull like head with sharp teeth and yellow, glowing, featureless eyes. It also has a number of long dark tendrils protruding from its back, and is clouded in what resembles black smoke.