You've manifested the icy might emblematic of frost giants, granting you the following benefits:
You have resistance to cold damage.
Immediately after a creature you can see within 30 feet of you hits you with an attack roll and deals damage, you can use your reaction to retaliate with a conjured blast of ice. The creature must make a Constitution saving throw (DC equals 8 + your proficiency bonus + the modifier of the ability increased by this feat). On a failed save, the creature takes cold damage equal to 1d8 + your proficiency bonus, and its speed is reduced to 0 until the end of its next turn. You can use this reaction a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.