Xenosaga Ep. I - Types of Enemies (B, G, ??)

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I've played this new game, Xenosaga Episode I: Der Wille Zu Macht, and since it's used, the game didn't have a game manual. Because I was hoping to find out what are these types of enemies: B-type, G-type, M-type, ??-type...I have no idea what they are. I've made it to the Gargoyle boss, yet, I have no idea what they are.