Jack is informed by a fisherman about the underwater city of Oceanus, which has a time machine, so Jack dives into the dark depths of the ocean, where he encounters the Triceraquins, the amphibious denizens of Oceanus whose city was sunken by Aku. There, the Triceraquins agree to let Jack use the time machine, but their real plans are far more sinister.
- Atlantis Is Boring: It's somewhat played with in that the Triseraquins complain that they haven't received any visitors since their city was sunk, as they seem to be the only people under the sea. However, the underwater realm itself is lushly portrayed as beautiful and full of strange life (there's a rather nice sequence during Jacks trip devoted to showing just how much weird stuff there is down there), and there's certainly plenty going on to keep Jack busy in Oceanus itself.
- And Your Reward Is Edible: To make up for their treachery and thank him for saving their lives, the Triseraquins give Jack some of their sushi, to which he happily eats later on as he's traveling.
- Easily Forgiven: Jack easily forgives the Triseraquins for selling him out to Aku and nearly getting him killed, as after all, few can resist Aku's wiles and trickery.
- Eaten Alive: After being shipwrecked, Jack is swallowed whole by huge fish. He still gets a good view of the outside world thanks to the fish's back being a transparent dome, and he manages to manipulate its nerve ganglia to get it where he wants it to go.
- Fish People: What the Triceraquins are.
- Giant Squid: Aku takes on this form to fight the Triseraquins' military when they try to fight him.
- I Did What I Had to Do: The Triseraquins didn't like tricking Jack and making him a sacrificial offering to Aku, even hesitating going through with the trap. Their reasoning was to have Aku raise their city back to the surface, as well as their livelihoods.
- I Lied: The Triseraquins capture Jack for Aku after he promises to remerge their city from underwater. Quite expectedly, after they capture Jack, he gloats he has "changed his mind", given them reason to free Jack as revenge.
- No Celebrities Were Harmed: One of the Triceraquins has a voice similar to Ringo Starr and is even named "Ringo" in the credits. It helps that he's voiced by Jess Harnell, who used the same Ringo impression for Wacko Warner.
- Organic Technology: The Triseraquins make heavy use of this — their vehicles all appear to be highly modified fish, and even the fake time machine and a good portion of their city are organic in nature.
- Time Machine: Rumors of one such machine are the reason why Jack seeks out Oceanus in the first place, so that he can return to the past and prevent Aku from taking over the world. Sadly, it doesn't exist — it was all just a trick to lure Jack into a trap.
- Trademark Favorite Food: This episode establish's Jack's love of sushi. The Triseraquins even give him a whole bag of the stuff to make up for tricking him.
- Underwater City: Oceanus, the city of the Triceraquins, built as a system of waterproof domes on top of high-tech towers. It used to be a City on the Water instead, but Aku banished them beneath the ocean to where their city is now. It returns to the surface by the end of the episode.
- Villain Ball: After capturing Jack in a bubble, he decides to, instead of crush him instantly, to leave a teeny crack in his bubble so he can watch Jack slowly drown. Of course Aku also decides to double cross the Tricerquins before Jack is dead, leading them to rescue Jack and set up his downfall.
- Worf Barrage: The Triseraquins throw everything but the kitchen sink to fight Aku, who either easily thwarts their attempts or just shrugs them off. This goes to prove that even in the future, Jack's sword is the only thing that can harm the evil shapeshifter.