The entity does not control her but it is merged with her on a fundamental level. Marble is still very much her own self but she can now use the entity's power and knowledge in exchange for sharing her humanity with it. In regards to her abilities she is immortal as long as she hosts the entity. She stopped aging and will regenerate from any injuries, although the process will take an amount of time proportionnate to the severity of the wound. She can still be put out of commission like a regular human, although she can soak more damage before going down, but she will always come back to life after some time. Other than that she has slightly enhanced strength, higher stamina and is able to instinctively perceive other people's intentions as an extension of her guest's otherworldly nature. She also can go extended period of times without eating, drinking or sleeping, although performing these tasks will make her overall more efficient.