The artbook gives a relatively large amount of information on Griffin, such as, "You could defeat it by making use of its weakness, fire. You were meant to fight it by riding Agro, as with Colossus 10." This could mean that it was afraid of fire, like Celosia, and swift like Dirge.
According to early sketches, "the joints are relevant and need to be redrawn" and that they "will act as obstacles". It also states that "the wings are for decoration".
According to unconfirmed information, it took a while to finally get on the colossus' back, and it was pretty easy to fall off. This is the reason it got scrapped, as it got frustrating and repetitive to keep getting on its back after falling off, which apparently took a lot of time.
Granted, though Griffin did not appear in the game, its location is highly speculated to be I7 on the map, due to the mountain wall there being similar to the one which is provided in several screenshots.