Katy Perry, John Mayer Vamp It Up At Early Birthday Bash

Kristen Stewart also helps Perry celebrate her 28th birthday during Halloween-themed party at Hollywood's Magic Castle.

Just days ahead of Katy Perry's 28th birthday this week, the pop star threw the ultimate Halloween-themed birthday bash at Los Angeles' Magic Castle over the weekend.

See photos of Katy Perry and John Mayer dressed up at Katy's early birthday bash.

Guests of the spooky soiree included Kristen Stewart (sans Robert Pattinson), Neil Patrick Harris, songwriter Diane Warren, "America's Next Top Model" creative director (and Perry stylist) Johnny Wujek and, most importantly, Perry's on-again boyfriend, John Mayer.

According to JustJared.com, Mayer took his costume as the vampire hunter to Perry's vampire very seriously. The 35-year-old guitar virtuoso appeared almost completely unrecognizable by sporting a prosthetic nose and chin to complete the look. The birthday girl's crimson lips, fangs and velvet cape made for the perfect sexy vampire, and the location couldn't have been more fitting: L.A.'s Magic Castle delivered a haunted-house vibe right in the heart of Hollywood.

Instead of gifts, Perry requested that partygoers make donations in support of the David Lynch Foundation for Transcendental Meditation, a charity that provides free meditation instruction to inner-city children and veterans. Urging fans to do the same, Perry tweeted, "Transcendental Meditation changed my life. For my birthday I would love to pay it forward. In lieu of gifts, donate."

It's been a week of bicoastal birthday celebrations for the reunited couple. Perry helped Mayer celebrate the big 3-5 at Freeman's restaurant in New York with a dozen of Mayer's close friends.

Perry turns 28 on Thursday.