Complex sentence: Despite this, Sif risks her life to travel to the realm of Mephisto to free what seems to be the soul of Thor from a mystical bag, she pledges her loyalty to the demonic entity.
Split into simpler sentences: Despite this, Sif risks her life to travel to the realm of Mephisto. To free what seems to be the soul of Thor from a mystical bag, she pledges her loyalty to the demonic entity.