At the end of the game during pre-Asriel cutscene when Sans shows up and Toriel recognizes Sans’ voice. That look on Asgore’s face lmao.
Also during the date with Alphys when you and her are role playing as Undyne+Alphys. No matter what you said, that part when Undyne comes in gets me every time.
And the call when Undyne said that she'll make everyones wishes come true and after paps dilogue(How do i spell) Undyne said that she'll make most people's wishes come true.
I liked the bit when you talk to asriel near the end after the barrier has been broken. When he says don't you have better things to do? He's like Frisk why you still here I destroyed the barrier just get on with it.
The dog ending, in which the annoying dog becomes president of the underground, due to you only killing major bosses, but no one else. Not even Sans has the slightest clue how it got there, but he says it "seems like the best life for everyone," before thanking you and hanging up.