C8 is a Takamimusubi fixed team challenge.
you can just to the color/orbs remaining part of the leaderskill to kill most floors. I made pseudo rows each floor and just blobbed what I could. For EKMD I popped the defense break, for Izanami-->unbind-->match jammers-->pop Taka-->pop kali if you need colors
for Apoullo pop the heart break and the other taka and match out. You'll need defense break to proc for a guaranteed kill.
C9 is a puzzle fight. Bring ALL the time extends. leaderskills and actives do not work, just TE awakenings. Match each color as a row and you'll be left with 5 rows one of each color. There's a couple quick solves for that. For me I picked up the second orb on the bottom left and snaked my way up only touching the left half of the board. There's videos on reddit and a couple diagrams but you can visit Dawnglare or use combo master to practice. I had 4.7 seconds to play with even loading up as many TE and TE equips that I could find.
C10 is kind of a pain. You'll want VDP, the ability to hit 10 combos, a fujin (or stalling ability), and some serious burst damage.
Floor 1 feels like a stalling floor. I killed ASAP cause I didn't want to deal with mechanics.
Floor 2 is rough, try to do 5% of Orochi's HP in the first hit so you don't get delayed (or have 4 SDR on the important skill subs.) Then kill on the second turn.
Floor 3 Isn't too bad, but a TE active helps a lot. The lead swap is annoying but stallable (a delay works first turn) VDP to kill or stall it out and chip to kill. It doesn't hit super hard but your HP might be too low post swap.
Floor 4 is Oichi, hit 9c to kill or die.
Floor 5 is DQ Hera, 169,792 preemptive hit, use a shield or have a lot of HP, or get rekt.
Floor 6 is Durga, Fujin + FUA to kill or stall and chip then kill.
Floor 7 is Revo Hinokagutsuchi. If you can end this fight quickly do it. You need to VDP + FUA 600million hp in one hit to do it. If you need to play then keep Kagu over 25% HP and break resolve then go for the kill when you can. If you drop it below 25% you eat a second 10 turn skill delay. If you pop resolve without FUA you eat a 10 turn skill delay and it heals.
If you have a meta lead this isn't too bad. DQ Hera will never not feel cheap though especially if you like to play dungeons blind.