Tamatoa is unpredictable and possibly insane. His mood tends to shift at the drop of a hat, going from cheeky and comedic, to murderous and menacing in a mere matter of seconds. He's quite monstrous in both size and attitude, one of his most well-known traits being his sadistic habit of eating anyone around him, be they humans, sea creatures or even gods—he even admitted to eating his own grandmother. Tamatoa is also quirky and comical, though in a dark and wicked sense. He has a twisted sense of humor, specifically shown when he nonchalantly commented that it took a week to eat his grandmother and blamed the delay on her enormous size in a joking tone. He also takes pleasure in torturing his enemies both mentally and physically, as shown when he playfully - yet brutally - thrashed Maui across his lair, while crushing the demigod's ego at the same time. With an apparent lack of boundaries, Tamatoa has no qualms with mocking someone's dead loved one, or exposing someone's deepest insecurities to amuse himself. Above all, Tamatoa is extremely narcissistic. With a superiority complex, he views himself as beautiful, and others as irrelevant and disposable. This is only surface-level, however, which actually serves as an antithesis between Tamatoa and the film's overarching message of identity and being true to yourself: Unlike Moana, Tala and Maui, Tamatoa does not believe in inner-beauty or "listening to your heart". Instead, he views anyone who is not physically attractive or outwardly strong as insignificant and lesser than him, albeit perfectly fit for a meal. This is his biggest flaw and ultimately causes his downfall, as he underestimated Moana's intelligence (because she's a human), which allowed her to best the villainous crustacean. Though he considers himself beautiful, however, he welcomes anything that will increase his power and, by extension, his social status, such as the heart of Te Fiti.
In the movie
Tamatoa is first seen during Gramma Tala's story concerning the mother island Te Fiti and her life-giving heart. According to Tala, many sought the heart for its power, and among these ancient entities was Tamatoa, though Maui was the only one capable of actually stealing the heart. In doing so, he was banished to a desolate island, while his fishhook was lost at sea in a battle for the heart against a wrathful lava demon. The fishhook would be recovered by Tamatoa, who added it to his collection of treasures. Later on, Maui is freed from his exile by Moana, who needs Maui to return the heart of Te Fiti to its rightful place. Maui eventually agrees, but needs his fishhook in order to accomplish such a goal. Moana and Maui travel to Lalotai, and the two soon find Tamatoa's lair. Moana is sent in as bait, covering herself in shiny objects to attract the crab. Tamatoa soon awakens, and examines the human that has entered his shell. Meanwhile, Maui reaches in to grab his hook, and although Tamatoa nearly notices, Moana is able to distract the crab by getting him to talk about himself through the song "Shiny". After Tamatoa brags about his shell and explains his love for all things shiny, he tries to eat Moana, only to pause when Maui reveals himself with his fishhook in hand. Tamatoa cowers in fear until he realizes Maui's hook is out of commission, crippling his ability to shapeshift. Tamatoa sadistically takes advantage of this by attacking and brutally thrashing Maui about his lair. When Moana tries to stop the cruelty, Tamatoa traps her within a cage-like plant. Soon enough, Tamatoa tries to devour Maui, but Moana escapes her cell and creates a phony duplicate of Te Fiti's heart. She calls to Tamatoa to show him the shiny prize in her possessions, and the crab immediately discards Maui in favor of his coveted treasure. He chases after Moana, who drops the heart in a crack on the ocean floor. As Tamatoa digs for it, Moana and Maui make their escape. It isn't long before Tamatoa realizes he's been tricked, and the enraged crustacean chases after the duo. They launch themselves onto a geyser heading to the surface, and the impact of the shooting water knocks Tamatoa onto his shell. Unable to move, he's left stranded on the ocean floor, asking if Moana at the very least enjoyed his song. Tamatoa is last seen after the credits, where he is still trapped and struggling to get off his shell, but to no avail. He asks the audience for assistance, and quips that if his name were "Sebastian" and he had a Jamaican accent, the audience would feel happy to help (a reference to the supporting character of the same name from The Little Mermaid.)
In the SAF series.
Tamatoa is promsied to be given an appearence in a future Cronicles episode yet to be desided to be given a season, where Junjie and his usual cronies team up with him and a Mothron myth cronicler, who's respondsable for reveiling the crab beast, who will allure him to going after Gazelle with the promise of keeping the "Shiny" Uniter blade, with being given Mothron magic to protect Tamatoa from being burned by the keyblade cause of clearly being evil by proxy on how mess-up he is mentally and moraly. However, even dispite that Tamatoa does give Gazelle a run for her money, the one thing Tamatoa can't just take away and placed it on his back and be protected from is her friends with the Lougers and the ZPD (Having Lightfly aide helps as well), which lead to the spell being removed by the keyblade being powered by Gazelle's love for life and those she cares about, which returns to her after burning Tamatoa badly, whch the bully quickly turned into a cowerd and is now the one overwealmed by Gazelle, where apawn defeat, now is being taken by silluettes of two certain folks from the Moana world to take him back to "where he belongs", implying that Tamatoa would never be able to leave again.... At least until Team Nefarious deside to go after him next.