Embodied by the cloak's everflowing form is the purest and most primal essence of water, flexible in small quantities yet unstoppable as a mass. Water seemingly spills from the cloak's collar onto the ground before evaporating without a trace.
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Cloak of Primal Water
Wondrous item, legendary (requires attunement)
While you wear this cloak, you have resistance to cold damage as well as a swim speed of 40 feet.
Form of Water. While wearing the cloak, you can move through an enemy's space without impediment, but cannot willingly end your move there. Also, squeezing costs you no extra movement.
Tidal Surge. The movement of your cloak compounds with your own. If you move at least 20 feet in a straight line toward a creature immediately before stopping in an unoccupied space within 5 feet of it, the cloak's water slams into the creature if you allow it. The creature must succeed on a DC 15 Dexterity saving throw or take 1d8 bludgeoning damage. A Large or smaller creature that fails this save by 5 or more is also knocked prone. A creature makes this save no more than once per turn.
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DESIGN COMMENTARY
I studied a bunch of artistic waves to get this one and I think it turned out pretty good! Like the Torrential Lash, I had also intended to draw the water as clear water to do some practice on it, but eventually decided the ocean colors are important. The cloak form developed during the sketch.
Edit: After some consideration, the primal element items have been altered to Legendary rarity instead of very rare. Damage resistance simply equates too easily to the rare armors.