I like this idea; it'd be nice to have shapeshifts that aren't textured mobs. However, as you said, this could be tricky as the Serpent/Snake model is a textured Diamond Spade with a decreased durability. The Shapeshift plugin is pretty flexible in my experience (Assuming that the plugin we use isn't custom), but it definitely seems like one small detail that would result in more suggestions regarding a Swooping Death, or a Occamy, etc.