The Insider.com

Things are getting pretty serious for Katy Perry and John Mayer as the two celebrated Halloween (and Katy's birthday) early, stepping out in costume together over the weekend.

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The photographer who goes by the name The Cobra Snake snapped shots of the on-again, off-again couple, who were eager to pose in their elaborate ensembles. Perry, who will be 28 on Thursday, was dressed as a vampire bride (Bella Swan perhaps?), while Mayer, 35, was a zombie hunter. Both singers pulled out all the stops for their characters -- the ET singer donned donned fangs, a velvet cape and red contact lenses, and Mayer showed up with a prosthetic nose and chin.

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The soiree was held at Los Angeles' Magic Castle with a star-studded guest list that included Twilight leading lady Kristen Stewart and Raising Hope star (and Perry's best friend) Shannon Woodward.