5 mages. Mirror Image gives you 3 copies per mage, and a 4th one with the appropriate glyph. So that's 25 in total here.

I went to AV yesterday evening. Quite fun. Nice little confusion amongst the horde.
My teams dies stupidly easily, though. So fast that no healing would help. They are just wearing the level 78 crafted set for now, it should get better with a bit of gear.