The episode introducing "Amulet Diamond", who quickly weaponizes her newly acquired power of music in spectacular fashion.
When Amu and Ikuto each gained both of their Super Forms for the first time, at the same time.
Screw that, the most awesome moments were Ikuto and Amu surviving what seemed to be A FREAKING MISSILE BLAST in the first season's finale, Character changed Kairi slicing a log in half WITH A WOODEN PRACTICE KATANA in order to save Amu, Yaya INGENIOUSLY using her duckies to help defeat an X-Egg corrupted dog, Rima reminding her parents that she has a life too, after years of marital arguments and overprotectiveness, and Ikuto, after transforming into his previously mentioned Super Form, staring downwards at his stepfather as the latter attempts, for the last time, to use the tuning fork that had been controlling him for around about half the second season, eventually throwing it on the floor and breaking it as he completely fails to do so. As insulin-cravingly sweet as this series is (not like that's a bad thing), the characters damn well do have a lot of balls.