We were walking through downtown late one night, when our eyes beheld an eerie sight. From inside Good Life (28 Kingston Street, Boston, 617.451.2622) we heard music arise — and suddenly to our surprise, it was the Monster Mashup (“It was the Moooonster Mashup!”): a Halloween dance party being thrown tonight by Bootie Boston, a collective of DJs who spin bootleg mixes and wild, clashing mashups that stitch together hooks from different songs to create all new Franken-versions (The B-52s vs. Soulwax, Lady Gaga vs. MGMT, and Prince vs. Michael Jackson are a few of the promised reinterpretations). And if you like what you hear, be sure to wear a full costume or, if you’re feeling less bold, some form of skull motif — if you do so, you’ll walk away with a free 10-track Halloween mashup CD. The $5 cover gets you access to two parties from 9 p.m. to 2 a.m., both this Bootie Boston bash downstairs and the upstairs floor’s usual Friday night Revolver party with DJs Brek.One and Ghostdad. This Monster Mashup sounds like a graveyard smashup, indeed. And if you're looking for more spooky shindigs, check out our complete Halloween event round-up here.