Tyga deserves an award for best-timed rebound ever, 'cause he's hooking up with UFC Octagon hottie Arianny Celeste ... fresh off Kylie Jenner's pregnancy news.

Tyga and Arianny were at Universal Studios Saturday night for Halloween Horror Nights. Witnesses tell us they were showing major PDA -- he wrapped his arms around her waist and she was holding onto him walking through the mazes.

We're told they're hanging out but are not exclusive. Maybe he needs a refresher on Arianny's vacay mode pics ... to lock down this relationship.

Perfect way to get over your ex getting knocked up, we're guessing.