for fur you could make him golden or blonde if im correct there is some mythology of a golden bull. not sure about nipple rings maybe a mini axe due to his toga having a mini axe. for tattoos and branding i feel like the greek alphabet could fit in nicely and you can also give Asterion the Taurus zodiac sign (i mean you can give him all zodiac signs but the taurus sign is the best fit for obvious reasons). also keep up the good work i love Asterion and the story and find it really engaging.