You summon bone shield that floats around you. While this spell is in effect, you gain +2 to your AC. When you take damage (other than Psychic), you may use a reaction to interpose the shield between you and the damage. If you do, the damage is halved. The damage reduced this way is calculated prior to resistances and after saving throws. If the shield reduces more than 20 points of damage from a single damage source on a turn, the shield breaks and the spell ends.