Claim is a bright red eye with a black cloud surrounding her.
Claim has a chance to appear when you open the door. You will hear a loud popping sound, which is her signal. If you start hearing a strange distorted buzzing or screaming sound, it means that Claim has completely appeared, and if you are in her field of vision, she will instantly kill you. As soon as the Claim fully appears, you should immediately hide.
She can't move. 
Many think Claim is a male, tho Claim is actually a female.