Wanted to test him out in a lenghtier fight like this and see how he does and how far i can go while trying to kill as many allies as possible.

First thing:

First phase of the boss is kinda a pita without some sanity restore at phase 1

Boss clashes like a mfer at the final phase

Things related to my team:

I used Mao Faust because i need a Thoracalgia user that also has pride and doesnt drop to low hp quick (so LCE Faust was out). Furthermore i deliberately didn't go for s3-2 spam as often as i could because this was just about testing the new Yi Sang in a lenghty fight (the damage tells you all how broken she is but you knew that already)

My team wasnt particular optimal and mostly a general somewhat hodgepodge of Pride and Wrath for the Fell Bullet ego, so mostly some poise and burn and Mao Outis as filler or something.

Now to things related to Yi Sang:
Getting ally kills is kinda a pita if you dont have low level units. You are basically have to let Sinners take one sided attacks to get them weak enough to kill them with either your Fell Bullet EGO or your s3 (this is also one of the reason why i had to hold back with Mao Faust). Using Faust's Thoracalgia EGO also slightly screwed me over because, as useful as the poise gain is, the heal puts some sinners i wanted to kill over the edge. His most notable trait though is the fact that Torn Memories from the EGO carries over into the next turn. This also means that you get full value of Torn Memories without resonance as soon as you have 7 (and 6 Pride ressources). This is also the fastest way to get to 7 Torn Memories after using your s3, or prepare 7 Torn Memories before using your s3 so even if you don't kill an ally, you get something out of it. He also hits pretty hard with his s1 and s2 with Torn Memories and is very reliant on his s1 and s2 for poise count.