Crystal Ward

You create 4 small crystal spears no larger than an arrow to hover in your space for the spell’s duration. When a creature that you can see within 30 feet of you makes an Attack roll, expend up to your maximum number of spears, making a spell attack for each spear that deals 1d4 cold damage and subtracting the number rolled from the creature’s roll per spear that hits. You can choose to use this feature after the creature makes its roll, but before the creature deals its damage.

At Higher Levels. When you cast this spell using a spell slot of 3th level or higher, the number of spears created increases by one for each slot level above 2nd.