Paris Hilton and boyfriend River Viiperi posed for photos before heading to the Playboy Halloween party last night, and once she got inside she tweeted, "#YES! @Iamdiddy killing it on the mike performing all his hits! #CirocFlowingAtThePlayboyMansion! #BestHalloweenEver! :D."

In addition to P. Diddy, stars like Chris Brown and David Hasselhoff were also at the bash ... click the gallery below for more photos!