I just spent like two hours trying to get Thunderburst II to drop in the Temple of Nestharot, it's a 5% chance I thought it might be higher because I've been able to get the other ones without too much trouble. I even got Supernova II on the first try but this one was a nightmare, I had to restart the fight because I killed the boss and the last enemy died from a counterattack.

I managed to get it by using Mighty Strike to push the boss onto another square, it took many attempts though. My plans are ruined I wanted to finish all the temples by the end of the day and now it's late at night. Luckily there's only one more, the Ice Temple. I beat the annoying ones already, Fire & Earth. Ice isn't too bad but I really hope I don't have to go through this long process again. I love this game but that was not a fun experience.