Would be cool to see nipple piercing jewelry made of bone instead of metal.
Don't make them in the shape of little femurs, that's too on the nose and even tacky.
Think more like this vvvvvv, one in each nip.
It's even one of the possible horn shapes for moos, so it kinda fits.
If you brand the moo, he probably won't like it. I hear that hurts.
Tats feel complicated for some reason. Does he have to shave his fur to see them, or do they just magically appear on top of his fur? Could be cool anyway. Imagine the player character and Asterion getting corresponding tattoos after a comfy evening of hanging out, drinking, and shooting the shit with a hotel guest only to find the guest is willing and able to ink you both up.
Give the "I Speedrun Games" playthrough some horrendous tattoo option like the pewdiepie logo or something.
Wait, no. Don't do that.
...unless?