Majors are enemies with a yellow health bar, while Ultras have the same, but they also have a skull icon on their info bar. Hive Majors can be found easily during the first of the missions on the Moon, The Dark Beyond, but it helps if you have the Heroic skull modifier active (basically play on a higher difficulty than the first one). I haven't been able to find a good source of Fallen Majors and Ultras, though the Strike on Earth has one Major and two Ulras (the Devil Walker and the Prime himself at the end).
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Majors are enemies with a yellow health bar, while Ultras have the same, but they also have a skull icon on their info bar. Hive Majors can be found easily during the first of the missions on the Moon, The Dark Beyond, but it helps if you have the Heroic skull modifier active (basically play on a higher difficulty than the first one). I haven't been able to find a good source of Fallen Majors and Ultras, though the Strike on Earth has one Major and two Ulras (the Devil Walker and the Prime himself at the end).