Palm Shields of Zeraf

Cantrip (This spell consumes no mana, but can
only be cast if you have at least 1 mana available
of the corresponding color. Only 1 spell with
Cantrip can be active at a time).
Once per round, you may roll a 1d20 against one
physical attack:
If result > 15 then Reduce Damage by 1
If result > 18 then Reduce Damage by 2