Armor of Agathys

Armor of Agathys, named after the sixth layer of Carceri, was a complex spell learned and used by young or inexperienced warlocks.

Effects
When armor of Agathys was cast, it created a layer of thick, black ice around the body of its caster, adding to their vitality for several minutes and injuring enemies who came too near with its frigid power. The deadliness of the ice depended upon the durability of the warlock. Armor of Agathys drew heavily on a warlock's power and it could only be cast once per day.

After the Sundering warlocks could cast it any number of times according to ability.

Stronger Spell
If cast at higher spell levels, the damage and vitality was amplified.

Components
A cup of water.