During research I made a list of tools and a list of weapons that I had not designed for yet, and the sling and wire cutter made for a perfect union - that along with the garrote use. Even though it's visually simple, I really like how this item can benefit your sneaky characters and really make use of the surprised condition.
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Few trained hands understand the unique uses of the cutting wire. Those with the finesse and dexterity to sculpt clay innately know the best the areas to leverage the wire's cutting edge without exerting great force.
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Severance Wire
Weapon (sling), rare (requires attunement by a character proficient with potter's tools)
You can use this sling as potter's tools for cutting clay. While attuned, you also double your proficiency bonus to ability checks made using potter's tools. Creatures unaware of the sling's properties initially perceive it as a simple tool and can use an action to recognize its true purpose by succeeding on a DC 15 Intelligence (Arcana or Investigation) check.
Pottery Sling. Ammunition fired from this sling is considered magical and deal an extra 1d4 damage to targets they hit.
Night Garrote. You can use the sling as a deadly garrote in stealthy situations. As an action, you can use two hands coil to the sling around a surprised target within 5 feet of you that is of your size or smaller. The target is grappled by you. For the duration of the grapple, a grappled target can only speak falteringly and takes damage equal to 1d8 + your Strength or Dexterity modifier (your choice) at the start of each of its turns. It also makes its ability checks to escape this grapple with disadvantage. You cannot use your hands for anything else while grappling a target this way.