Brace

When you are required to make a Dexterity saving throw you may instead use your reaction to brace against the attack. In lieu of a Dexterity saving throw, you may make a Strength or Constitution saving throw equal to the Dexterity save DC + 2; on a success you gain resistance to the damage type received and negate the remaining damage by a value equal to your Armor Class. On a failed save, only negate the damage by your Armor Class. 

You may use Brace a number of times equal to your proficiency bonus per long rest.