Do you remember the movie where the heroine wakes up to a mirror image enemy that copies her every move and she tries to escape but the mirror image follows her, ultimately suffocating her by copying her every move while she fights it? The only way she defeats it is by playing dead or something, lying on the ground, then laying a bomb/grenade on the enemy because the enemy is a copycat but does not have any of the equipment except the heroine's physical structure.

It was in a room with sand, the copycat might have been one of many obstacles; the movie was not too old (like 2000's +), and the girl might have been Natalie Portman.