What even is this dungeon layout
Anyway, I'm currently up to 15F, though I'm not exploring it until this last boss on 14F (in the east) is over and done with. I've currently recruited Suika, also cleared 13F with the help of a guide (I suck at math, go sue me lol)
On the Eientei fight: I managed to clear it, partly with a few adjustments (
like adding Tenshi) but mostly with a LOT of luck. My strategy was to keep all three bosses alive, but paralyzed and poisoned and then try to knock them off at the same time (or at least kill Reisen last, because she's least threatening / easily paralyzed compared to Eirin and Kaguya) and it... mostly worked.
Actually trying to keep all three alive is easy ironically enough because of Eirin's heal spell. Her healing Reisen and Kaguya lets you know when they're on low health, lets you avoid accidentally killing Reisen or Kaguya by accident (and eating a desperation spell to the face) and lets you know when to start wailing on Eirin (as Eirin has the most health of all three bosses). Once Eirin's down, Kaguya will go down quickly too (she has half of Eirin's health value, and even Eirin's healing can only do so much) leaving you with Reisen (who is not a problem if you have one the following characters still alive to paralyze her: Reimu, Cirno, Yuugi, Suwako or Komachi. It's even easier if you have two or even three paralysers to keep her down, like I did)
The luck based part mostly comes down to what Kaguya and Eirin are doing while you're trying to drain all three characters health down. Kaguya has several AoE's can cause problems (like Fire Rat Robe which will destroy Cirno), Eirin also has a few AoE's and a very problematic Magic Drain attack that can hit at the worst moments. I was lucky as Kaguya didn't use FRR, and Eirin mostly just used her single target spells against a buffed up Tenshi, but things can go bad pretty quickly if Eirin wants to be a jerk and sap all the SP off Patchouli after you just switched her in.
Tbh this was not my favorite boss to fight. The fact that Kaguya and Eirin (and also Reisen) have so many attacks that can screw up your party in so many ways (mana draining, poison, silence, multiple elemental AoE's) is way too much tbh, even the paralyze strategy doesn't work so well if Eirin decides to just never get poisoned or paralyzed (which happened a lot). The fight just feels way too random for my liking.
I'm hoping the later bosses are a bit less random / more consistent to handle (so more bossfights like Alice and Tam's Foe, less like Youmu and Eientei)