It doesn't appear on its own I believe, are you running from every battle that isn't Page 256? Because there are a few different sequences of Page enemies (you beat one, then another one appears, and so on) and some but not all of them include Page 256.
Mating with duck is like vomiting in a too small bucket. Listen to my music: http://www.newgrounds.com/audio/view.php?id=907376
I had some trouble getting this guy's Blue Magic too, because I came back to the Library right as I was about to leave World 1, and found that a lot of my attacks just killed the "Page" monster outright instead of making it cycle. If you're trying to get Off-Guard, you probably want to have your Control user Hasted, because Page 256 likes to use Moon Flute to Berserk your entire party early in the fight. It's really frustrating when he finally appears and your party just beats the hell out of him. :\