As I read this, I'm thinking that maybe we need to have a thread or even a post for bystanders/collateral damage characters! So everyone who wants to be involved can, even if they're not on the main thread -- for people like Duo, who will want to try and help but shouldn't be in the main event (mainly because trying to organize 10 people to thread would be impossible ;;).
What are MOMO's attack capabilities? I don't know her canon so it's hard to tell if they'll injure him. Spiritually based or astral attacks hurt him the most, if that helps.