Amplifying Focus

This Arcane Focus is attuned to a particular elemental damage type. When you cast a spell that deals the attuned type of damage, you may reroll one damage die. You must take the new roll. 
1 - Acid
2 - Cold
3 - Fire
4 - Force
5 - Lightning
6 - Necrotic
7 - Poison
8 - Psychic
9 - Radiant
10 - Thunder