Yes, let's reduce Dex to 11 and increase NA to +13. That sound ok?
The many-finned version is statistically done after that, I think, though it probably should have a separate description.
Tactics for the many-humped: These sea serpents bite their prey but flee when significantly injured, diving long and deep to avoid their opponents.
Seems like it depends on whether it's a "grazer" like the baleen whale or a predator. They seem a bit more frightening as sea serpents if they might mistake a small boat for some type of prey.
Works for me. Do you feel the need for anything separate for the many-finned version?
These sea-serpents attack by biting. If they feel their lives are threatened, they lash out, impaling foes on their spikes. ???