If the players put on the mask without adding their blood they must make a constitution saving throw, DC 10
Success=they will take 3d6 fire Damage as the mask heats up on their face and burns off.
Failure=the mask will fuse to the players face, 3 tries to remove the mask DC 11 DC 13 DC15 and must make two successes. After two successes the wearer takes 6d6 fire damage and the mask falls off. If they do not meet the requirements the mask is fused to their face and their mind is controlled by the original creator of the mask like a golem.
When wearing the mask under the proper attunement they can control what expression is on the mask. This gives them advantage on deception checks.