Armor of Agathys

Source: Player's Handbook (2024)

1st Level Abjuration (Warlock)

Casting Time: Bonus Action Range: Self Components: V, S, M (Cup of Water) Duration: 1 hour

Protective magical frost surrounds you. You gain 5 Temporary Hit Points. If a creature hits you with a melee attack roll before the spell ends, the creature takes 5 Cold damage. The spell ends early if you have no Temporary Hit Points. Using a Higher-Level Spell Slot.
The Temporary Hit Points and the Cold damage both increase by 5 for each spell slot level above 1.