- Ambiguous Gender: Just like its source material. Though in The Leave Option in the Pacifist Run. Frisk is refered to as a little boy by a kidnapper.
- Big "NO!": When Sans tells them that they will never be able to finish the fight due to Sans never taking his turn.
- Comical Angry Face: It's Sr. Pelo, what else did you expect?
- Humiliation Conga: Has one in the Genocide ending.
- Little "No": Has 2 of these before their Big "NO!" for the reasons mentioned above.
- Screw This, I'm Outta Here!: When Toriel asks if they'd like to say goodbye to everyone before leaving the Underground, Frisk high-tails it to the surface instead.
- Slasher Smile: Sports a few. One when chasing Flowey with a knife, the other when trying to kill Sans in his sleep.
- Catchphrase: "Too bad!"
- Explain, Explain... Oh, Crap!: When he monologues to Frisk in the Genocide Ending, he states that neither of them would hesitate to kill the other if they got in their way. While standing in Frisk's way. His first words after he fully realizes this are "Oh, shit...".
- Foul Flower: His original counterpart is the provider of the page image
- A Handful for an Eye: Throws pocket sand into Frisk's eyes as an attack.
- Calling Your Attacks: Sans calls his last volley of attacks the "Sans Dance"... at the top of his lungs.
- Hero Antagonist: Like in Undertale, he's the final obstacle Frisk faces in the Genocide Route, and is giving it his all to stop Frisk from destroying everything.
- Megaton Punch: His first attack against Frisk
- Suddenly SHOUTING!: When he announces the SANS DANCE, he does so at the top of his lungs.
- Butt-Monkey: Asgore is treated as this in All Three Videos/Runs.
- Memetic Mutation: Him sounding like Waluigi makes him become this. It's funny as all hell.
- The Voiceless: Except for One Scream. She doesn't have a speaking line.
- Oh, Crap!: When Papyrus mentions he got help getting the main 6 monsters together by a "tiny flower".
- Creepy Child: Shows up to destroy the world, and causes Sr. Pelo to freak out completely.