Frisk is the main protagonist of Underfell and the eighth fallen
child of the Underground. In the True Pacifist run, Frisk is accompanied by Flowey as they try to escape the Underground alive, trying to negotiate out of danger and reform every monster they run into. Although not as common in fan content, in the Genocide run Frisk is shown as being tired of being pushed around, hurt, and worse, and as a result decides to kill every living thing in the Underground before erasing humanity.
Many fans like to interpret Frisk as having been bullied and abused at home, as a result running away and accidentally falling into Mt Ebott, although, less commonly written, it is said that Frisk was abused at home and jumped into the Underground on purpose, wanting to end their own life. Other interpretations of the Underfell story place Frisk as the canon Undertale Frisk after completing a True Pacifist run, having entered a corrupted or otherwise changed version of Undertale after a bad reset. This version of Frisk, as well as Flowey, are canon in the Underfell fan game.
Frisk is a small child of indeterminate age (though most see them as a child around the age of ten), race, and gender, matching their Undertale counterpart. They have short brown hair, usually illustrated as a bob or bowl cut.
Although usually depicted as wearing the same clothes they wear in the Undertale game, some artists make Frisk distinctive from their canon counterpart by putting them in a black and red striped sweater, with dark red pants and black shoes.
Frisk's personality is dependent on the type of run that they are shown participating in. In most interpretations of a True Pacifist run, Frisk is kind, friendly, calm and caring, as well as extraordinarily forgiving. Frisk refuses to hurt anything and will always find a way to get out of a dangerous situation without violence, despite the behavior of the monsters. Occasionally this kindness is interpreted as silliness, naivety, or even stupidity on their part, which is, in that case, commented on by Flowey.
In No Mercy runs, Frisk is determined to survive and escape the underground with Flowey by their side, even it means killing some boss monsters (but not all of them). Frisk is also a good friend to him. In the Genocide runs If they chose to kill all the monsters, Frisk becomes dark, cold, cruel, evil, selfish, aggressive and easily enraged. This is where the monsters (including Flowey) became disturbed by their behavior. They sometimes exhibit bullying behavior rivaling the cruelty of the monsters underground, and kill without hesitation and, often, without saying a word.
Powers and Abilities
As in Undertale, Frisk has the power of Determination. This power allows Frisk to survive death and heal themselves when severely injured. Frisk is also usually shown to be very good with their reflexes such as when avoiding attacks.
If Frisk kills a monster, Frisk gains their soul power and grows stronger in strength. If Frisk doesn't kill anything, Frisk is proven to have the ability to negotiate out of danger by being nice the right way.
Undyne: Undyne attempts to kill Frisk, but begins to question herself after being shown mercy several times. Or, alternatively, works with Frisk, in versions where Undyne is against Asgore.
Asgore: Asgore attempts to kill Frisk, but will eventually be killed by either them or Sans, depending on the run chosen.
Flowey: Flowey is Frisk's initial friend during the game, accompanying them across the Underground.
Alphys: She continually tries to kill Frisk as they journey through the Underground.
Mettaton: Mettaton attempts to kill Frisk because Alphys demands him to. In the True Pacifist run, he will kill himself when the calls are taken.
Napstablook: Napstablook attempts to kill Frisk in the ruins.Monster Kid: Monster Kid hates and bullies Frisk throughout their journey in Waterfall.