What Do You Call A Group Of Ninjas?

From AskMeFi: “You know, like gaggle of geese, murder of crows, school of fish, all that. Does a group of ninjas have some sort of descriptor? We’re talking many people in halloween costumes, how to address them together. The { blank }.â€
Aside from the inevitable brush to Ask a Ninja, answers included:

sir, sir, sir, and [...]

namiacs

mr. pro-life and his wife, kirsten faith pro-life
names, pro-life, politics