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Tenna appears as a 3D-rendered humanoid figure with an old TV for a head, lacking any facial features aside from a wide, often-grinning mouth and a long, pointed nose. His attire consists of a flashy red suit with twin coattails, a long yellow tie, black pants, large cartoony white gloves, and bright yellow dress shoes. He is taller than both King and Queen. Tenna is an upbeat and energetic show host who thrives on entertaining his audience by both flattering and challenging his contestants. Beneath his lively persona, however, he is deeply insecure and egotistical, prone to panicking when things don’t go as planned. He recalls fondly how, as a television in the real world, he once brought Kris, their family, and friends together to play games and watch shows. Now feeling abandoned, Tenna struggles with feelings of worthlessness and loneliness, and fears that he’s no longer interesting and that he’ll be discarded.

When confronted about his age, Tenna adamantly denies being "old." After the Trio discovers Toriel trapped inside a toy capsule, he spirals into panic and reacts by imprisoning them in capsules as well. His outbursts often turn destructive; he lashes out and fires his employees in bursts of anger, driven by his overwhelming fear of being left behind and forgotten.

Despite this, he is shown to have a kind heart. Part of his motivation for forcing the Delta Warriors into his show was simply so that he could entertain them. He has a strong desire to entertain and bring people together. While he even expresses frantic concern over Toriel, doing everything he can to assure she doesn't wake up, this is because he worries his overall plan of appeasing the Knight may fail. His desire to entertain, while apparent enough to make one trust him, is also rooted in wanting to help the Knight succeed in taking Toriel. This conflict of wanting to help the Knight but needing the attention from the Lightners is what ultimately makes him change for the better.

Tenna is also seen to be rather enthusiastic and patient, as if you lose the physical challenges multiple times, he'll always end his dialogue with "One more try! Let's CHALLENGE again!" demonstrating his confidence and faith. Tenna makes his appearance shortly after Susie lashes out at Ralsei early in Chapter 3. He immediately forces them into becoming contestants for his game show, "Mr. Ant Tenna's TV Time!" Susie initially refuses, causing him to grow sad. Ralsei, still wanting to have fun with her and Kris, convinces her to give in, bringing Tenna's mood back up. He leads them over to the right so they can prepare for the show.

After the trio pick their names, Tenna introduces the first round: A 'board' of his game "The Legend of Tenna." To win the board, the three must find three keys throughout the game. Tenna provides commentary as they play. After they manage to open the door to the pyramid, Tenna transports the trio to the board's physical challenge: The Cooking Channel, where the trio are tasked with feeding guests while avoiding rolling fireballs.

After the first board's completion, as the credits start rolling, Tenna roundhouse-kicks away the roll and desperately announces the existence of a second round in order to keep the show running. After a sponsor segment, Tenna introduces the trio to the Green Room before leaving. If the player manages to obtain a T-rank (the highest rank possible), a special room opens up in the rewards room, where Tenna is seen rotating in a t-pose while doing a double peace sign.

Before the second round, Tenna is seen talking to someone who is presumably sending messages through Tenna's antennas, before noticing Susie. Tenna ends his conversation and asks Susie what she needs. Susie responds, thanking him, as the whole experience seemed to cheer up Ralsei, as well as being fun for her. Tenna expresses joy at the fact that he was able to entertain them both. Susie mentions that Kris was having fun too, but Tenna has doubts. Upon being notified that the next round is about to start, Tenna hurriedly ushered her back to the Green Room. The trio is then brought back to the stage as Tenna introduces the second round, another board of "Legend of Tenna". This time, the player will have to take 3 special photos and reunite 2 lovers at Lover's Peak to create a path to Atlantis Stadium. During the game, Tenna receives a message through his antennas, and temporarily leaves, allowing Susie to swap her controller with that of Kris, and potentially even Ralsei's as well, while no one is looking.

Eventually, Tenna returns, but then leaves again right as Lanino and Elnina are about to "reunite" (this was not the case, as it was unexpectedly foiled by a forced union with and by Rouxls Kaard), then returning right as the trio enters Atlantis, he introduces the second physical challenge- Lightners Live, a rhythm game where the player controls Kris playing the guitar.

After the completion of the second board, Tenna will express sadness that it was the final round. However, as the credits roll, Tenna reveals that the three have unlocked the requirements for the secret bonus round. Ralsei initially refuses, but after seeing how depressed Tenna got, Susie agrees to play it, just for a little bit, which causes Tenna to perk up.

Tenna can still be found on stage, talking to someone through his antennas. Susie, along with Kris and Ralsei, come in initially to let Tenna know that they can't stay for another round after the bonus, but overhearing his conversation causes Susie to become skeptical and return to the Green Room. Returning to the stage with Kris will initiate an awkward conversation between Kris and Tenna. Tenna will attempt to end it and leave, but not before asking Kris if they could bring over Asgore and Asriel so that they can watch him together.

After the party finds Toriel, Tenna begins approaching, so they hide behind her gachapon ball. Tenna, upon reaching Toriel, expresses relief she is still asleep, not knowing what he would do should she wake. He tells her he's sorry he has to keep her captive, but he has to in order not to end up thrown away. He picks her up, presumably to present her as the grand prize of the gameshow, when he finds the party hiding behind her. The screen then changes to "Technical Difficulties". When the screen returns to normal, Tenna and the party are back on stage. Tenna introduces the next round as if the run-in had never happened, but Susie, fed up with Tenna's antics along with the fact that he's holding Toriel captive, tells him that they're done playing and to return Toriel to them. Ralsei agrees with Susie (albeit more gently) that they need to seal the fountain and that the show has gotten old. This angers Tenna, causing him to trap the Delta Warriors in custom-made gachapon balls, forcing them to watch as he plays the third board for them, subjecting them to quizzes that adulate TV, battles where the only option is to ACT, and modified versions of Physical Challenges.

Eventually, Tenna slips up and brings a Zapper to one of the fights, where the party is able to use it to pull a disappearing act on him, leaving behind only the empty gachapon capsules on the battlefield. Tenna, distraught at this turn of events, worriedly asks where the party members went and ends the battle, now desperately searching the area for the party.

Tenna can be seen berating his employees for failing to find the party, almost firing them in rage, so he docks their pay until they're found. Though they wish not to fight the party, Tenna reminds them that it's part of their contract to listen to his orders and follow him off-screen.

If the player manages to find Tenna's bonus zone, he can be seen angry at the multiple Pippinses raiding his points. Tenna tries to stop them by mentioning their contracts, but is unable to find them. He gives up and lets them, claiming he has something they'll never have, before going to the room on the right. If you follow him into it, there will be a blue safe. Opening it will reveal a Pipis inside. If the Dealmaker or the Puppet Scarf was obtained, Tenna will then come back into the room, causing the party to hide in the room on the left. Upon finding the Pipis was discovered, Tenna is distraught, wishing he had someone to help him, even accepting the help of "that spammy mailman". At this, the Dealmaker/Puppet Scarf will come out of the inventory and turn into Spamton. Tenna, not recognizing him, freaks out. Spamton tries to explain, but Tenna sprays him in foam and takes the Pipis away.

Tenna can later be found in the area after the Rouxls Kaard fight, where his employees begin leaving him one by one. He blames it on a "spammy little mailman" again and begins to panic. In the next room, Elnina and Lanino leave him, too. He lets them, claiming the Lightners won't get far without the weather channel, but then panics again upon hearing about apps. Even Mike announces that he's leaving, too.

After returning to the Green Room and making your way through the code-locked doors, the Lightners will come back out in the Cold Place and attempt to make their way to the Dark Fountain, only for Tenna to drop from the sky, attempting to convince them to just "Return to their seats". Susie refuses, questioning why he's so desperate for them to play in the first place. Tenna reveals that Kris' family, before recently, had gradually stopped watching him, causing him to become lonely from neglect. He then reveals he's been working with the Roaring Knight, who promised that if he kept the three of them busy, he'd have all the people in the world to watch him. He wishes not to be thrown away, or to become irrelevant. He attempts to start another round of his game show, but Susie attacks him in anger, initiating a battle.

After defeating Tenna, he shrinks in despair, afraid to be thrown away. Ralsei tries to soothe him, telling him he still brought joy and smiles to Kris' family and friends, and that even if he does get thrown out, all Darkners become obsolete eventually, and that they shouldn't make the Lightners worried about them. This only makes Tenna sadder. Susie then moves Ralsei out of the way, and tells Tenna he doesn't have to take being thrown away. She begins to tell her story, of how she always felt like a broken toy no one wanted to play with. Every time she did make a friend, she ended moving away. She then explains that since she got to Hometown however, her life has gotten better, and how she just needed to find the right people. She and Kris even agree to find someone to adopt him. This causes Tenna to become overjoyed with hope, telling Susie he'll make a hall of fame just for her, even agreeing to give back Toriel, despite it not being what the Knight wants.

The party follows Tenna to the christmas tree, where he presents Toriel as their grand prize. Not too long after however, The Knight slashes off both of his arms, punishing him for disobeying, and he falls offscreen.