I have found that the EM elemental damage (or anyone that causes earth elemental damage) crits every time.

The toad is water based

earth > water

before the level 3 immunity the def/res reducing chases/attacks/mysteries helped, but now, not so much.

also, earth passives 1-2 and 2-1 give shields and increase nin/atk by 30% (better than LM 25% atk)

just run EM 2nd mystery every other round and your squad will ALWAYS have a shield, which means 30% nin/atk the whole fight