well because it's so easy to make it resemble an archon ! Go in trigger editor, and do this :
Archon live Events Unit - A unit enters (whatever Region) <gen> Conditions (Unit-type of (Triggering unit)) Equal to Archon Actions Special Effect - Create a special effect attached to the origin of (Entering unit) using Abilities\Spells\Human\ManaShield\ManaShieldCaster.mdl
and here you have your archon. Simple, no ? It doesn't look EXACLTY like an archon, but who said it was obliged to ?