Well he is using 3 characters so there is really only 5 exotic drops with decent chances. 1. Weekly Nightfall 2. Gorgon Maze Chest 3. Atheon 4. Ir Yut 5. Crota But something else to consider. Both Atheon and Crota drop exotics on both normal and hard so if you run both raids on both difficulties you are actually upping your chances, effectively creating 2 extra exotic drops. Meaning 7 per character, 21 per week if you have 3 characters