Elemental Shield Runestone

uncommon

Item

A suit of armor or a shield

Description

When you first affix this rune to a suit of armor or a shield, choose one of the following damage types:

• acid
• cold
• fire
• lightning
• thunder

While wearing (armor) or wielding (shield) this item, whenever you take damage of the chosen type you can use your reaction to reduce the damage by an amount equal to twice your character level + your Constitution modifier and suffer one level of exhaustion.
You can change the chosen damage type over the course of a short or long rest by spending at least 30 minutes in contact with the runestone.