Level 1 Abjuration (Warlock)

Casting Time: Bonus Action
Range: Self
Components: V, S, M (a shard of blue glass)
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.

Armor of Agathys

1 Abjuration

Casting Time: Bonus Action
Range: Self
Components: V S M (a shard of blue glass)
Duration: 1 hour
Classes: Warlock
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.
At Higher Levels: 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.