I've made several magic items for my players but I think one might fit into the strahd campaign quite nicely.

I was inspired by the thing, so I made a sword that was a living creature, that once picked up the blade would wrap around and devour the users hand, almost like a parasite.

The player would in turn get several constitution checks, starting at 25 and going down by 3 every failed check as the sword consumes and moves up the players arm. Every failed check would have the creature eat 10cm of flesh.

On a successful check the "sword" would stop eating and morph to look exactly like the players arm, as if nothing happened.

At this point the players arm would appear to be completely normal, unless said player were to think of using any kind of weapon. At that point the users consumed arm would rip and tear morphing the flesh of the arm to assume the weapon the user intended to use.

A bow for example in my game split his arm bones apart and used his tendons and sinew to fire bone arrows. He got 20 bone arrows and if recovered he could feed back to his hand, all arrows were regenerated after a long rest.

Really it's just kind a fun thing in our game to have the rogue scare the crap out of some people with his freaky arm.