The Crimson Bands of Cyttorak is a spell that is dependent on a demon called Cyttorak. By tapping into the power of Cyttorak a sorcerer can summon mystical strands of energy that combine to form a mystical force field.
When Cain Marko found the Gem of Cyttorak, the gem released the Crimson Bands of Cyttorak which transformed Marko into the Unstoppable Juggernaut.
Baron Mordo used the Crimson Bands of Cyttorak to protect the Center for Reunification. However, Doctor Strange was able to invoke the Hosts of Hoggoth to remove the Crimson Bands of Cyttorak and he, Wong, and Spider-Man went inside to battle Baron Mordo.