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.