The image is cheesy, but that's classic Scooby Doo for you.
Requirements fit, save for the stone dragon requirement, especially considering the whole "must be on land to use these abilities" nonsense for the school. Note that I personally dislike the resurrection requirement, but it's Halloween, so that's expected.
Still needs skills, preferably four plus with swim present.
HD, BAB, and saves all look in order.
For proficiencies, you should also give them Light and Medium armor, if only on the off chance someone gets in without either.
Maneuvers and schools look in order.
Deep Shell makes sense and isn't bad, especially for a nautical campaign. The encumbrance is a nice, albeit minor plus.
Watery Grave is nice. Free swim speed and an odd subtype. Not bad. You should probably add "You may treat water as earth for the purposes of using Stone Dragon maneuvers and stances."
Blackwater Blood is nice. Free out of combat healing is always a plus.
Blackwater Body hits with Deep Shell.
Dredge Line reminds me of Bloodstorm Blade. Not much else to say.
Nautical Lights isn't much, but it helps shave the costs off of sunrods.
Wounding Strikes is nice. Free +2 weapon property and an extra +2d6 are very nice.
I'm having a hard time with rating Bring Them Down. There already exists a slew of maneuvers that work via ranged attacks. Having more is nice, but it seems to counter the bonus from Wounding Strikes.
Frozen Abyss just means packing some extra fire resistance. There's already precedence with throwing mortals subtypes anyhow with the frozen/flaming rage feats. Not bad.
I feel like Reel Them In should be an earlier class feature, but otherwise love it. Also, isn't there a different harpoon that does just this?
Love Brutal Impalement. Insuring hurt is always good.
Having Unstoppable's regeneration stopped by positive energy seems odd to me, but that's about it. Solid class feature, for sure.
One With the Depths is a solid capstone.