Although she is the "final boss", Agartha is in my opinion the easiest one by far. https://imgur.com/a/6dg2k (Note that it's Levitation, Equip on Gatz, and Levitation, All on Gego) 2 Grand Rags (on Bahl^ and Snaip^) Minidra on Gatz^ Doesn't really matter what you put on the other 3, but I just used my remaining grand petas. Pincer the adds on the first turn (if you put them in the same order as me and move with Gatz, it's really easy). Double pincer Agartha vertically on turn 2, making sure Bahl and Snaip hit last (or do a triple if the remaining add cooperates). Use all taps and double pincer on turn 3, making sure Bahl and Snaip hit last. You won't have a PP, so hopefully your heavy hitters have high SB. Agartha will drop to 1 HP, disable all of your skills, and summon a bunch of adds. Pincer Agartha on Turn 4 and she'll die (if the Schweiz bombs didn't kill her already). The first clear will give you the Debilitating Light otomo, which gives you a 1-charge defense impair (not that great). The only other noteworthy reward is that the 100L chest can drop a Skill Candy with about a 25% chance.