I know this isn't Undertale, but I wanted to share this anyway. There is an anime called Assassination Classroom, aka AssClass, about students, part of the End Class (the students with the worst grades in the school), who must assassinate their teacher, who is a flying octopus that blew up the moon. Though he must be killed, the students get attached to him for he is an amazing teacher. Throughout the seasons (there are 2), more professional assassins come to kill him, some helping the students and some not caring if they die in the process. The principal of the school, Mr.Asano, is strict to the point where it's wrong. Everyone above the End Class is to learn things many grade levels ahead of them, including his son who is the leader of the A class, and destroy the E class at any cost. 

This song is dedicated to Mr.Asano himself, for he was a terrible teacher who displayed a fake friendly smile.

~ 

There's a hole in your logic,
You who know all the answers, (Oh-oh-oh-oh)
You claim science ain't magic, (Oo-oo-oo-oo)
And expect me to buy it

Goodbye Mr. A,
You promised you would love us, but you knew too much,
Goodbye Mr. A,
You had all the answers but no human touch,
Your life is subtraction,
Your number is up,
Your love is a fraction,
It's not any more

So busy showing me where I'm wrong,
You forgot to switch your feelings on, (Oh-oh-oh-oh)
So, so superior, are you not,
You love a little bit but you forgot

Goodbye Mr. A,
You promised you would love us, but you knew too much,
Goodbye Mr. A,
You had all the answers but no human touch,
Your life is subtraction,
Your number is up,
Your love is a fraction,
It's not any more

Goodbye Mr. A

Goodbye Mr. A,
The world was full of fun until you opened my eyes,
Goodbye Mr. A,
Wish you hadn't pulled my mind and killed the surprise,
Goodbye Mr. A,
You promised you would love us, but you knew too much,
Goodbye Mr. A
You had all the answers but no human touch.

Your life is subtraction,
Your number is up,
Your love is a fraction,
It's not any more