Shapechanging Weapon

[Fightmaster]

I'm trying to design a magic item for an npc that allows them to be good with any weapon and generate said weapon. I'm not sure the best way to do it, as the players will most likely try to take it and I don't want it to be overpowered when they do get it. They will most likely not have access until level 6 at least. Do you have any suggestions for how to best do this?

[HoarsHalberd]

I'm trying to design a magic item for an npc that allows them to be good with any weapon and generate said weapon. I'm not sure the best way to do it, as the players will most likely try to take it and I don't want it to be overpowered when they do get it. They will most likely not have access until level 6 at least. Do you have any suggestions for how to best do this?

Have it be sapient(sentient), and when its previous mastered is injured it shutters itself in whatever form it was in at the time, whilst it tests the party to find a suitable new master, announcing it's intentions to the party when picked up.

[PhantomRenegade]

You could say that the part of the weapon's power that allowed the user to be good with any of its shapes died out with the NPC and just give them a otherwise normal shapechanging weapon requiring a action to change shape.

They still need proficiency to use whatever form its in but its still kind of a nifty weapon to have.

[Anderlith]

Living Weapon: this weapon can change form into any weapon from the weapon list as a bonus action.
Attunement: When wielded by the weapons owner, it also grants proficiency on melee attacks with itself only.

[pwykersotz]

I'm trying to design a magic item for an npc that allows them to be good with any weapon and generate said weapon. I'm not sure the best way to do it, as the players will most likely try to take it and I don't want it to be overpowered when they do get it. They will most likely not have access until level 6 at least. Do you have any suggestions for how to best do this?

Have it be a physical focus for a bladelock pact. The patron controls the shape and it otherwise behaves much like the feature. You can limit it as much or as little as you want based on the patron's goals.

[darkscizor]

Let it turn into any simple weapon as a bonus action an infinite number of times per day, or into any martial weapon up to 4x per day, and the owner of the weapon who is attuned to it gains proficiency with said weapon.