Crystal Barbs

When you are hit by a mele attack you can use your reaction causing small clusters of crystals to form around you. You add [roll]1d4[/roll] to your AC until the start of your next turn. If you are hit by a mele attack before the spell ends the crystals shatter and deal piercing damage equal to the AC you gained from the spell. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the AC bonus increases by 1d4 for each slot level above 1st.