From an adventurer’s perspective, ocean giants are like storm giants, just…more so. More tempestuous. At CR 14, more powerful. And with the vortex spell-like ability and a 50% chance to be chaotic evil, way more likely to drag the entire party down beneath the waves to drown or be crushed in the depths.
Essentially, it’s the difference between Zeus and Poseidon. Zeus had his moods, but they came and passed like storms. Poseidon’s curse, on the other hand, haunted Odysseus for 10 agonizing years—a surly supernatural malice that battered against everything and everyone Odysseus came in contact with, like waves against a rickety dock. Ocean giants are like that—even the chaotic good ones are slower to anger but take far longer to return to brooding calm, and the evil ones rule by fiat, fear, and fists clenched in covetous rage…for decades.
Since losing his family’s conch shell horn to a triton in an ill-considered bet, Millainus Stormcaller has stewed below the waves, obsessing over the loss. When the triton enters a race from Bronze Isle to Breakneck Bay, the ocean giant finally sees a way to retrieve his horn without losing face. Efforts that foils his plans, particularly from meddling land-walkers, will be met with rage that eventually boils over into outright murder, all thoughts of saving face swept away in the angry tide of the giant’s wounded pride.
In Acacia, storm giants are exceedingly rare, born only from cloud-ocean giant unions. When Don Vaxos’s storm giant son prepares to wed a cloud giant maid against his wishes, the ocean giant takes it personally, using an ancient ritual to drag the entire festhall to the bottom of the ocean. The son has just enough time to scream a message to a roc ally, who in turn races off to find the only adventurers she trusts. Now it’s a race against time to rescue the cloud giant wedding guests from the sea floor before their air runs out.
Festooned in spines and barbs, the Palace of Urchinheart was never a welcoming place. But ever since its ocean giant lord fell under the sway of a kyton envoy, it has become a place of nightmares. Now sailors vanish beneath the waves to fuel ever-darker rites, and the lord’s household is in turmoil preparing for his marriage to a kyton termagant who appears part woman, part armored whale, part metal sea scorpion, and part bloated anglerfish.
—Pathfinder Bestiary 4 127
Apparently I like wedding adventure seeds today. Also, I’m pretty sure that first adventure scenario also involves asp cultists, griffon riders, and a vortex of radiant violet water, but I don't know how.
Also, a great model for both storm and ocean giants is the Master of the Straits from Jacqueline Carey’s various Kushiel novels.
If you’re looking for the nymph water strider, we covered it back here.