Etherealness

[DeadlyShoe]

Generally speaking your mages should never be taking arrow fire if you have deployed correctly. It's not impossible, but your astral mages are usually better employed either killing the enemy or buffing your troops... AKA arrow catchers.

The most common reason mages take arrow fire is that they are too close to archer groups; enemy archers set to Fire Archers can and will scatter arrows onto the mages.