Playboy Mansion -- Big Bash All a Dream to Hef

The soon-to-be-sold Playboy Mansion hosted the annual Midsummer Night's Dream party Saturday night ... and Hef was nowhere in sight.

Truth be told ... the event was celeb light -- only a handful showed up. Kris Humphries, Too Short, Alan Thicke and a few others mingled. But lots of hot chicks.

This is Hef's last stand as the owner of the Mansion. It sold to 32-year-old businessman Daren Metropoulos. Hef has a right to live out his life there before Daren comes in with a sledge hammer.