Armor of Agathys (updated)

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.

*This is an attempt to deal with an error on the original spell that prevents its inclusion in homebrew species.