Magic Item: Cloak of Shadows

This dark hooded cloak is cool to the touch and always smells faintly of damp earth (being created from used grave shrouds, it makes sense).  Detect Magic reveals transmutation and necromancy magic.  Those that look for it also finds the Cloak of Shadows radiates mild Evil and milder sentience and malevolence.

Donning the cloak does nothing, but pulling the hood up over your head provides the wearer with several traits of Shadows, nominally the amorphous and shadow stealth traits.  Removing the hood brings the wearer back to reality, which can be fatal if in a place to small for their body.

However, malevolent, necromantic, and evil magic always comes at a cost.  

Image found on Twitter, by Lemoris Ashcraft @infernalshroud

In this case, the cost is as follows:  after each use, there is a cumulative chance that the wearer becomes a proper shadow, with the cloak detaching and falling to the ground in heap.  

Each wearer starts at 0%, and adds 1% per hood-donning. When the wearer goes to remove the hood, percentile dice are rolled, and the if the numbers come up at the percent or lower, the wearer moves to NPC status as a full free-willed shadow.  At this point, the wearer's gear falls from shadow into physical space with a clatter and thump, the Cloak of Shadows atop the pile.  

In addition, keeping the hood up for too long can add to the cumulative percentage.  If the wearer stays hooded for more than one turn, they suffer a level of exhaustion for each turn or fragment thereof.  A PC that dies from exhaustion inflicted by the Cloak of Shadows becomes a shadow, drifting free of its belongings as its mortal frame turns to dust.  

From 0% thru 49% the Cloak of Shadows is just a useful tool for sneaks and scouts.

At 50% a remove curse spell is required to remove the cloak; unhooding requires a DC12 Wisdom save; the Shadow trait of Sunlight Weakness takes hold, so the wearer suffers disadvantage on attack rolls, ability checks, and saving throws while in sunlight. 

At 75% the cloak whispers to the wearer, suggesting being used.  This plays out with the GM directly asking the player if the PC uses the cloak.  The unhooding save increases to DC 14.

At 80% the unhooding save increases to DC 16.  The Cloak whispers to the PC in dreams and when alone; long rests are disrupted by nightmares if the PC fails a DC 12 Wisdom save. 

At 90% the unhooding save increases to DC 18.  The Cloak's sentience and malevolence becomes active, and unhooding saves are at disadvantage.  Nightmares are a DC 14 Wisdom save and continue even if the PC successfully gets rid of the Cloak of Shadows.

At 99% the unhooding save becomes DC 20 at disadvantage as the Cloak is screaming into the PC's mind to join it in Shadow.  

At 100% the PC becomes a shadow as described further up post.

Nether Shadow, Christopher Rush, 1993 Magic Card

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GM Note: the GM can keep the growing number a secret if that is their jam, or they can create suspense and tension and paranoia by having the player keep up with the number, but not telling the player why.

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Something like this may already exist, and if so, someone please let me know.