Armor of Agathys

Armor of Agathys was a complex spell learned and used by young or inexperienced warlocks.

Effect
When Armor of Agathys is cast, it creates a layer of thick, black ice around the body of its caster, adding to their vitality for several minutes and injuring enemies who draw too near with its frigid power, the deadliness of the ice depending upon the durability of the warlock. Armor of Agathys draws heavily on a warlock's power and it can only be cast once per day.

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

Stronger Spell
If used within higher spell levels, the damage and vitality is amplified.

Components
A cup of water.