The bird-mask fiends in the hallway after the crystal skull are no problem but I'm having some major trouble with the groups (bird-mask fiends+ Van-Gelfs then bird-mask fiends + scythe fiends) after...
What's a good way to kill bird-mask fiends, scythe fiends, and flying Van-Gelfs, especially when they are in the same group?
For Van Gelfs, they are super fragile. A quick strong combo to kill them off is great. Archfiend's YYYXXX was my go-to move, and it's last 2 button presses hit surrounding enemies. Though you may not have upgraded that weapon, so experiment with what you do have.
When it's just birdmasks you can run around and charge UTs. If you see an opening for SoB, take it.
Void Ninpo is great since it fills quickly. See if you can line up enemies in a clump, including the scythe fiends.
I died many times here. Good luck and I hope you can glean something helpful from my post.