Thor, about your request:
Ability name: Fire Armor
Levels: 6
Effect: Creates a shield of fire around a target friendly unit, that adds him 3/6/9/12/15/20 armor and burns nearby enemy units, causing 10/15/20/25/30/40 damage per second. Lasts 30 seconds.
Target type: Unit Target (Automatically)
Special Effect: Immolation Target
Cost: 50 mana
You want to it cast automatically ? look like frost armor, inner fire, etc?