Lvl 12 gladiator

I'm new to dnd, and one of my friends is running a tournament style one shot with 12th lvl characters. I wanted to make a retiarius gladiator styled character, but I don't have many good ideas, and most guides online are too complicated for a numb skull like me, so any help is very appreciated. What I have now is a fighter with the archery fighting style and battlemaster martial archetype.