Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
"Victini's odd typing leaves it weak to weak to Aqua Jet, Shadow Sneak, and Sucker Punch, but resistant to Mach Punch, Vacuum Wave, and Bullet Punch while being neutral to the priority Normal and Flying-type moves."