Yeah in my second attempt I barely damaged Mari going into the final phase and it was probably what killed me in the end, as I did what seemingly felt like a million in damage and she never died

But yeah my Mari party was Meiling, Reimu, Ran (first time using her for the game), Iku (first time using her for bosses), Alice (tanky build), Rinnosuke, Youmu, Nitori, Suwako, Kaguya, Komachi and Patchouli.
My party for traversing the dungeons was Meiling, Ran, Alice, Rinno, Youmu, Nitori, Suwako, Kaguya, Komachi, Patchouli, Orin and Mokou/Flan
Now that she's done I'm half-grinding, half-playing around with other characters. Seeing if I can fit Yuyuko into the team to help with 20F mobs.
Otherwise some of the V2's are kicking my ass right now, I'm Reimu 143 so that feels like it shouldn't happen but it's happening. In all fairness, I'm not using any strategy I'm just nuking them to death with no preparation, so that might have something to do with it.