** From Kobold Press' Deep Magic by Dan Dillon, Jeff Lee, and Chris Harris**
You have mastered the special powers of one rune. Choose one rune that you have already learned through Rune Knowledge. You can invoke one of its mastery powers, provided you meet any other requirements such as a minimum level.
You can select this feat multiple times. Each time you do, you learn the mastery powers of a different rune from your repertoire.
Invoking Rune Powers
Invoking one of a rune’s powers requires an action and provokes opportunity attacks. Generally, you must either create a physical representation of the rune (in paint, in blood, drawn in the dirt or snow, and so forth) or trace the shape of an existing carving of the rune that was created to an exacting standard.
Each rune confers a benefit on someone who knows how to scribe it. A rune’s benefit is always in effect for a character who knows that rune. In addition, that character can call upon one of the rune's powers when so desired. Unless otherwise noted, any rune power can be used once, and that expended use is regained when you finish a long rest.
Some powers have a level requirement (given in parentheses); when a character attains that level, this power becomes an additional choice. Mastery powers are a separate category: only a character who has the Rune Mastery feat for a particular rune can use its mastery power. If a power or a mastery power has no level requirement, it becomes available to you as soon as you acquire the necessary feat.
If a rune’s power gives you the ability to cast a spell, you can do so without needing any components (aside from materials needed for the drawing of the rune), and the spell is always cast as if using the lowest-level spell slot possible. It typically has the same duration as a normal casting of the spell, and uses your character level as the caster level. When a rune power calls for a saving throw, the DC equals 8 + your ability bonus + your proficiency bonus. Typically, the ability that applies to the DC calculation is the same as the ability used for the saving throw.
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