This'll just be a small idea but hopefully I can get across what I thought of correctly.
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What Is It?
This will allow for players to create custom weapons, or modify the ones already inside of the game.
The player will be able to:
Change Hilt Size.
Change Blade Size.
Add Misc Parts For Stylisation On The Weapon.
Color The Different Parts.
Change The Type Of Hilt, Blade and Guard + Pommel.
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How Would This Be Balanced?
This would be balanced as the things that directly change the weapon itself [Hilt, Blade, Guard And Pommel size.] would increase the cost of the weapon, having excessive parts to your weapon [Extremely Large Blade + Hilt] would both increase the weight of the weapon aswell as increase the cost by A LOT more than if you were making a medium sized weapon.
Furthermore, when creating a game, you can enable an option to either allow or prevent custom weapons into the game.
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[THIS IS JUST A ROUGH SUGGESTION OF WHAT COULD BE, THINGS CAN BE CHANGED IN FAVOUR FOR THE DEVS.]