Similar to a Zombie Mask, the Mummy Mask is completed by giving a female a temporarily blinding facial. Once said female has been blinded, she will get up and stumbled around the room with her arms raised searching and moaning for a towel.
The variation between a Zombie Mask and a Mummy Mask occurs when amidst her Zombie stumble, you throw pieces of toilet paper into her face, thus giving her the appearance of a mummy.
Bro, did I see a mummy coming out of your room last night?
No, that was just Sarah, I mummy masked her.