I believe your idea is a good start but you should definitely plan the creature around an event race, a guild locked creature race is pushing it a tad bit. Either way, I wish you luck. The origins of your lore conflict with the Druidic Shapeshifting magic, I'll link you it here so you may see what I might be getting at.
https://wikia.lordofthecraft.net/index.php?title=Shapeshifting_Magic