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My son's going to be Bowser for Halloween this year.

You can view and edit this part online: https://tinkercad.com/things/ihcZLXtPWsd-bowser-bracelet

Measure the wrist that will be wearing this right below the thumb at the widest part.
Scale up the unit test bracelet and print to be sure it will fit and sit well.
Scale up the unit spiked bracelet the same and print it.

(Full disclosure, there is some overhang issue at the top, but it's good enough for me.)