Actually, X. Drake has an Ancient Zoan that lets him become a Dinosaur. o3o
Then again, I could also go with a Mythical Zoan that allows the transformation into a White Wolf who controls the Sun (So, fire, heat, that stuff) or Nature (Plants, etc.), Ala Amateratsu from O-Kami.
And..I dunno how I would moderate his power. lol.
But, as with most Zoan users (Especially now) I'd figure that he would have had said powers long enough to control his transformation more, thus being able to only change certain body parts at a time if he wished.
You've also go to understand that the Yamato no Orochi is MASSIVE (like, Literally, it's full form would take up at least 1/8 of a Normal Island. Lol) So..he probably won't go into Full Form that often if I choose to go that route.
But yeah..Hybrid form would be something like sprouting Dragon heads, Tails, Feet, hands..scales, etc, etc.
Of course, at full power, said scales would be as hard as steel..with one vulnerable spot (As with most dragons) where the scale is reversed. o3o