God mutator/settings?

Earlier today my steam friend invited me to his listen server. He and I were invulnerable to enemy/self/fall damage and could move extremely fast. The problem is he somehow enabled perk leveling as well. I didn't witness the perk progress going up myself, but he said his headshot count was still increasing. I don't have any information about how/where he learned to do so because he obviously wouldn't tell me, but I thought I should report this.