Serenity (formerly named Impenetrable Defense) is a Defensive Monk skill unlocked at Level 16. The Monk summons a holy shield to protect himself from damage.
The Monk expends spirit energy to summon a holy shield which protects the caster from incoming damage.
 Skill Rune Effects
The following is a very quick summary. See the Serenity rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
|| Cost: 10 Spirit|
Cooldown: 20 seconds
You are enveloped in a protective shield that absorbs all incoming damage for 3 seconds and grants immunity to all control impairing effects.
|| Reap What Is Sown
|| When Serenity ends, the shield explodes, dealing 30% of the damage absorbed by Serenity as Holy damage to enemies within 20 yards. The damage to each enemy cannot exceed 100% of your maximum Life.
|| Extends the protective shield to allies within 45 yards for 1 seconds, and makes them immune to control impairing effects like Slow and Frozen.
|| Instant Karma
|| While Serenity is active, 50% of all projectiles and melee attacks are reflected back at the attacker.
 Skill Design
The following Monk passives provide a benefit to Serenity:
Serenity was first shown (as Impenetrable Defense) at BlizzCon 2009 as one of the originals when the Monk was unveiled. Flux was able to try it out:
This one was not needed in the Blizzcon build, since the Monk was quite overpowered in combat. I didn’t experiment with his “dodge” ability, which is mentioned as a by product of several skills, since it was so much more fun just to blast everything with his offense. Plus, testing time is always limited, even in the press room. I would have made sure to try the other element of this skill, the “rebounds enemy ranged attacks,” but there were zero monster archers and virtually no projectile spell casters in the Blizzcon build.
It was slightly modified and renamed to Serenity in the game demo that was presented at BlizzCon 2010 as a Tier 2 skill.
Skill tiers were removed shortly before the beta started in September 2011, and Serenity became a level 18 skill. The skill system was once again overhauled for the Beta Patch 13 in February 2012, and Serenity was classified as a Defensive skill and moved to level 16. For Beta Patch 15, the cooldown on Serenity was greatly reduced.
 Previous Versions
See Impenetrable Defense for the original version of this skill.
Serenity can be seen in action on video here:
You can find pictures in the Diablo III screenshot and picture gallery: