One of the fun things about Kill Team is that your Leader can roll for extra abilities and special rules after each game. On Day 1 of the League my leader, Inquisitor Contrebis got: +1 leadership; Fleet; and Stealth. He also had Fleshbane from the beginning.
I have tried adding things to the model to symbolise these bonuses and abilities (and will continue to do so throughout the time of the League - Contrebis should be quite a sight by the end...)
Brother Overkill got a Silver Skull for shooting an enemy Leader (an Ork).