Aegis of Shielding

For the duration of this spell, you have advantage on Constitution saving throws that you make to maintain your concentration on this spell when you take damage. You place a mark on a creature that you can see within range. It is aware of this mark. If that creature was already marked, this mark replaces it. Until the spell ends, if that creature makes an attack that doesn't include a creature with an active Aegis spell or the Sentinel feat, is has disadvantage on that attack. If that attack hits and the marked target is within 50 feet of you, you can use your reaction to reduce the damage dealt by that attack to any one creature by 1d4 + your Constitution modifier.
If the target drops to 0 hit points before this spell ends, you can use a bonus action on a turn of yours to mark a new creature.

Higher Levels: When you cast this spell using a spell slot of 2nd level or higher, the damage reduction granted by your reaction increases by 1d4 for each slot above 1st.