A custom painted Mimic Dice Box

We’ve all been there. We just rolled up a 1st level (pick a class). How do I make him/her/it stand out?

There are lots of ways to do this. Good places to start could be an interesting backstory, an unusual preference for an odd weapon/spell/ armor combination, that ‘one thing’ that’s unusual, odd, or just plain “Whaaaaa!?!’ Some editions of D&D address this to an extent but in general it’s not a priority.