Armor of the Abyss

You call forth a swirling vortex of abyssal shadows, which engulfs you and nearby allies, reinforcing your defences at the cost of divine interference. You and any creatures of within 20ft of your choosing gain 5 temporary hit points and 3 AC.

When a creature with the AC increase takes damage from an attack, the creature that attacked them takes (1d4 + Number of corruption points necrotic) hit points of damage.

When cast at higher levels:  The amount of hit points gained increases by 1 for each spell slot level above 1. The damage the enemy receives is increased by 1d4 for every spell slot level above 1.