Bark Shield

Armor (shield), rare (requires attunement by a druid or ranger)

This wooden +1 shield is covered in bark and moss.

Radiates: Abjuration and transmutation magic.

Power: Whenever you suffer a critical hit, the bark magically expands to block it so you take no damage.

The excess bark then explodes in a 15 foot cone in the direction of the attacker whose critical hit was blocked.

All creatures (not just hostile ones) within the cone take 3d6 piercing damage (Dexterity save for half).

Creatures wearing metal armor save with advantage.

You may use this power a number of times per day equal to your proficiency bonus.