I was going through 70% blind (occasionally looking things up like items, armor, how to get places) and screwed up that fight by telling Moore to stay sad early in the dlc and losing my shot at his armor (after I finish the DLC I'll probably go kill elden beast again to get the things I missed in the DLC by winging it).
I had Thiollier and Sanguine Noble available to summon as collaborators. I did look at guides to do Thiolliers quest line and I don't think I would have figured it out without them. I have no idea what I did to make Sanguine Noble available.
I did bring Hornsent into the Messmer fight and Igon into Bayle, half for the rp aspect and half because I needed the distractions for the bosses.
Allegedly you keep your shadow fragments if you kill elden beast and come back to the DLC in ng+, so you can come back and hit +20 easily instead of hunting around the map for the last few fragments one may have missed.