And UNDERTALE TEAM thanks you, the player, from the bottom of our hearts. Without you, all of this would be impossible.
Involvement in Story
Before the player starts the game, they name the first human and not the protagonist.
The duality of the protagonist and the fallen human is not revealed until the epilogue of the True Pacifist Route or (if slightly less clearly) the Genocide Route. Throughout the game, characters do not refer to the protagonist by name and instead call them "human" or "child."
In the Genocide and True Pacifist routes, Flowey calls the protagonist by the player's chosen name. Flowey and Asriel are the only characters to do this; Asriel names his sibling in the True Lab VHS tapes and before his battle.
LV relates to the number of monsters killed, and higher levels of LV make it easier to harm others. Because LV and EXP display under the player's chosen name in the Stats menu, they increase the fallen human's ability to harm others.
At the end of the Genocide Route, the protagonist does not require a SOUL to attack. The player loses all control over the protagonist as they autokill Asgore and Flowey. The Bullet Board does not appear for either of these encounters.
Certain characters could be addressing the player in some scenes. For example, after the True Pacifist Ending Credits, Flowey appears and speaks into the fourth wall with no bullet board or ACT commands present.
Flowey begs for the world to be left alone and recognizes that the power to reset everything can still be used. However, this dialogue is up for interpretation because Flowey ends the conversation by addressing the fourth wall as the player's chosen name.
Another possible example is at the end of the Genocide Route when the fallen human speaks into the fourth wall. Again, this is up for interpretation as the fallen human uses "you" as opposed to a proper noun; they could be speaking to the protagonist.
One interpretation is that the place where the fallen human meets the player is in the protagonist's inner self, where the fallen human scares the player - the jumpscare only occurs if the player tries to resist their will.
Disabled Player Control
While the player usually conducts the protagonist's actions, there are moments in the Neutral Route and the Genocide Route in which control of the protagonist is temporarily disabled, and the protagonist performs actions independently from the player.
- During Sans's introduction, he instructs the protagonist to go through the bridge after telling them about Papyrus. The protagonist crosses the bridge on their own, with Sans following closely behind. This also occurs on the Genocide Route.
- The protagonist automatically hides behind the conveniently-shaped lamp when Sans directs them to it and comes out when he tells them to.
- The protagonist automatically follows Papyrus as he leads them to his house.
- In Papyrus's house, the protagonist attempts to catch the Annoying Dog as it escapes from the sink leading to the Dog Shrine.
- During the hangout with Undyne, the protagonist follows Undyne to the stove during her cooking lesson.
- In the Throne Room, the protagonist walks forward on their own, alerting Asgore as he is watering the Golden Flowers. This also occurs on the Genocide Route.
- Before the battle with Photoshop Flowey, the protagonist takes a step forward as if to defy him.
- The protagonist does not hide behind the conveniently-shaped lamp when Sans asks them to.
- During the puzzles with Papyrus, the protagonist seems to ignore Papyrus, and walks forward independent from the player.
- During the confrontation with Papyrus, the protagonist continuously walks forward on their own, and Papyrus notices and comments on it.
- Before the battle with Undyne the Undying, the protagonist turns away and then approaches Monster Kid aggressively.
- During the two encounters with Mettaton, he notices the protagonist's eagerness to fight him.
- During Sans's judgement, the protagonist takes another step forward to provoke him into fighting.
- With no player input, the protagonist deals the killing blow to Sans after he dodges the player's final attack, dealing 9999999 damage.
- In the Throne Room, the protagonist forcibly engages combat with Asgore.
- Um... what... What IS your name? "Frisk?" That's... A nice name. - Asriel
- The more you kill, the easier it becomes to distance yourself. The more you distance yourself, the less you will hurt. The more easily you can bring yourself to hurt others. - Sans
- Everyone will be ripped from this timeline... ...and sent back before all of this ever happened. Nobody will remember anything. You'll be able to do whatever you want. That power. I know that power. That's the power you were fighting to stop, wasn't it? - Flowey
- You've probably heard this a hundred times already, haven't you...? Well, that's all. See you later... <Name>. - Flowey
- Greetings. I am <Name>. Thank you. Your power awakened me from death. - The fallen human