He is a pale young man with dark, messy, fluffy hair that often falls over his eyes. He is almost exclusively seen wearing a simple, dark grey hooded sweatshirt or sweater. He wears a distinct silver cross necklace, highlighting his devout Christian faith. Due to an alternate invading his room when he was six years old, Mark lives in a constant state of hyper-vigilance and fear. He is generally quiet, isolated, and highly cautious, keeping his distance from others to ensure his own safety. Despite his profound fear, he is deeply protective of his friends. When his best friend Cesar calls for help, Mark overrides his own caution to drive to Cesar’s house. Mark relies on his faith as a shield, frequently praying or turning to scripture during moments of extreme terror. Ultimately, it is the Alternate mocking this deeply held faith that shatters his psychological defense. Mark Heathcliff was trapped in his bedroom for three days because he was being stalked and psychologically tortured by an Alternate.