Mana Shield

You use your Encounter Start action to give yourself Mana Shield, which gives you Temporary HP equal to your Toughness + 3 or Focus + 3 (whichever is higher). 

Wearing armor reduces this to 2/3rd, 1/3rd or 0 if wearing Light, Medium or Heavy Armor respectively. While Mana Shield is active, you do not provoke attacks of opportunity from casting Spells from enemies that are Challenged by you.

Until the end of the encounter, at the start of your turn you may spend 1 mana to restore your Mana Shield to its maximum value. (With similarly reduced values for wearing armor)

If you did not use this as an encounter start, you may also spend 1 AP and 1 Mana to activate this.