Agrianian Assault Infantry

[keravnos]

They fought along the hypaspistai (elite hoplite inf) in Gaugamela. There they were 1000. Alexandros considered them among his best and most trusted troops. Their land was pretty much next door to Makedonia and Epeiros. So, how could we NOT have included them?

http://en.wikipedia.org/wiki/Agriani

Alexander made heavy use of them: indeed, every time he dispatched a flying column the Agrianians were always included. They were supplied by the client king Langarus. They were expert fighters in mountainous terrain where the phalanx was impracticable

[Geoffrey S]

Their commando use is what they were famous for, but that by no means indicates they didn't have a significant (numerical) presence on the battlefield, unlike say the Arcani in RTW.