For total concealment, I'm not sure what other than masks would make sense. Though if you have suggestions I'm open to ideas. For things like train robberies or strikes on the Ministry, I don't think we would care about pretending to be someone else so much as just hiding. I've been thinking about some sort of illusionary fog or swirling colours hung on a simple mask.

If we want disguises there are lots of other options and you're much more the expert on those.