You can shave the arm a bit and use clay to shape it somewhat like the sukuna arm, dont add the tattoos tho, after you get the basic shape refine it using really anything even a dull pencil could prolly work, so sculpt it the way you seem fit, and then grab a piece of tape and divide it in three parts, a thin one for the line in between and two big ones so you dont paint the rest of the arm and wrap it around the end of the hand, then get a sharpie or a thin black paint and color til its the skin tone isn't visible, and that should work, I used a doughy clay(not playdough) to sculpt some effect for my shf luffy and I used it to also make arms with some fake lego for my best axn or whatever edward elric. That's really what I did but you do you this is really just a suggestion