Alright... Long story short, I made a manual save before trying to attempt the Aerial Predator achievement. Anyway, after a few tries an achievement popped, so I moved on. Now, I went back to check through my achievements, and Aerial Predator is not unlocked; and in its place (or at least same date I thought I unlocked it), is "Slayer." Well, I am almost positive that I read "Aerial Predator" when the achievement popped... So possible glitch (they were obtained at the exact same time, or not, and screwed things up; or mistake and coincidence? Unfortunately, I saved over the manual save file :(
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