By far clearing the master challenge for the Circus Facility event. It's the most frustrated the game has made me, I literally threw my phone at one point from getting so upset. I only had H!Edward as a decent light DPS and had promoted him to 5 stars just for the event and still couldn't do it. I was getting so sad and frustrated I had given up on it.

A few hours before reset I decided that I owed myself taking a few more cracks at it and I finally beat it with Rawn as my only surviving unit. Literally cheered out loud at 1:30am EST and woke up my roommate. A mobile game has never made me that excited before. That's when I knew this game was something special.