Prior to the Sword & Shield chapter, Casey obtained Tera as a Toxel. Tera first appeared in a flashback in PASS05–now a Toxtricity–traveling with Casey to the Slumbering Weald to obtain a Wishing Star. Upon finding the Wishing Star, Casey and Henry found themselves surrounded by the Legendary PokémonZacian and Zamazenta. Tera attacked them with the rest of Casey's team, though the moves passed right through the Pokémon. Realizing they're illusions, the two humans walked through them, only to be knocked out by a bright flash of light. After waking up, Casey realized her entire team had gone missing.
In PASS14, Professor Magnolia found a Sinistea and Polteageist hiding in her mobile home from a Pokémon that attacked them in the Glimwood Tangle. When Allister and Casey went to the same location later on they discovered a hurt Dreepy. The culprit was quickly shown to be Tera, who, in a fit of rage, failed to notice its Trainer and continued attacking the Dreepy. It was then revealed that the Dreepy was being taken care of by a Drakloak, which used its speed to get the better of Tera. Once the mushrooms in the area stopped glowing, however, Tera was able to lure the Caretaker Pokémon into a false sense of security and defeated it with Snarl. With its rage over, Tera happily rejoined Casey.
Tera battling Opal's Alcremie
Tera was one of the three Pokémon Casey brought to use in her gym battle against Allister, where it ended up being defeated.
In PASS18, Tera was used as Casey's final Pokémon in her battle against Opal, going up against her GigantamaxAlcremie. Casey decides to Dynamax right away, only to discover Tera is able to Gigantamax. Happy with the unexpected power boost, Casey and Tera attack with G-Max Stun Shock, poisoning Alcremie. Alcremie counters with G-Max Finale, though Tera takes it head-on, confident in its ability to resist it. Although it takes little damage, the onslaught of cream missiles ends up confusing it. Tera then knocks itself out. Because of this, Casey is eliminated from the Gym Challenge.
Personality and characteristics
Like its Trainer, Tera is very energetic and headstrong, as seen when it ran headfirst into a gate. It likes to pick on opponents it thinks are weaker than it and show off, but goes into a rage if they turn out to be strong. This arrogance can also hurt it in a fair fight, shown when it lost the match against Opal's Alcremie because it focused only on how much damage it could take instead of the side effects of the attack. Tera's bass-like sound from its electrical organ is unique among its species, sounding like a bass slap. It has a strong relationship with Casey, able to snap itself out of its rage at the sound of her voice.
Tera's sweat is poisonous enough to hurt itself, something which aids in fueling its rage. While Gigantamaxed, this poison is amplified to the point it can poison others just by being near them. It is able to store and release millions of liters of poison while in this form.