"masquerader, mummer," late 15c., agent noun from guise.
Why Do We Say “Trick or Treat”?It's many kids' favorite part of Halloween. There’s no feeling quite like waiting for a stranger to open their door so you can scream the words "Trick or treat"! But, why do we say it? What does it actually mean?
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for guiser
This guiser's mode will never do to enter the city of Amersfort withal!Lochinvar|S. R. Crockett