Well, Arc-Rock is quite true, but:
+2 252 Atk Parental Bond Kangaskhan Sucker Punch vs. 252 HP / 0 Def Giratina-O: 495-585 (98.2 - 116%) -- 87.5% chance to OHKO
+2 252 Atk Parental Bond Kangaskhan Crunch vs. 252 HP / 0 Def Giratina: 423-501 (83.9 - 99.4%) -- guaranteed 2HKO after Leftovers...