Crimson Cloak

Blood is the currency of life, and it is natural to covet this wealth.
You pull blood from the open wounds of those around you into your cloak, infusing it with stygian magic. Whenever you or a creature within 15 feet of you loses hit points, your cloak gains a blood value equal to the amount of hit points lost, to a maximum total of 30. Whenever you would take damage from a spell while your cloak has reached the maximum blood value, you can use your reaction to gain resistance to the damage you would take from the spell. Once you do this, the cloak’s blood value returns to zero.

At Higher Levels: When you cast this spell using a spell slot of 5th level or higher, the maximum decreases by 5 per spell slot level above 4th.