Mariah Carey, I Still Got Tricks Up My Sleeve (PHOTO GALLERY)

Mariah Carey went retro for her big Halloween bash ... she was squired by her ex and left her fiance at home.

Nick Cannon was front and center with the twins, along with a ton of celebs ... including Master P, Floyd Mayweather, and Tiny Harris.

As for James Packer ... we're told Halloween parties just aren't his jam.