Grayswandir Opportunity Attack

When wielding Grayswandir you gain the following benefits:

• While you are wielding Grayswandir other creatures provoke an opportunity attack from you when they damage you with a weapon or spell attack.

The opportunity attack does 1d6+3 damage (you do not add any proficiency or other modifiers). At Level 10 the damage increases to 1d8+3 and at level 15 the damage increases to 1d10+3