Undyne-the-Undying:

Deep down in my heart I feel a burning passion 
Deep down I can feel the power that's inside
Deep down in my heart I feel DETERMINATION 
Deep down there's a feeling that won't let me die

With all that I got
I'll strike you down
Even if you stop, it's too late now
This is the end, I'll be your last
monster that you can't get past.

If I ever let you go, I know that my friends will leave me.
If I ever let you go, then all the hope will disappear.
But I will never let you go, everybody's heart beats in me.
I will never let you go, everybody's goal will be fulfilled.

I will [bad word] away, even if you see me falling.
But if I ever fall, I know she will be there watching over me.
I will never give up hope, 'cause I've got my friends behind me.I know that this world will live on.

Mettaton NEO:

MY [bad word] FORM IS [bad word] AND JOIN MY FANDOM.
BUT WITH NO FANS STAR CANNOT MAKE IT FAR.
HUMANS AND US MONSTERS SEE YOU AS THREAT.
AND THERE'S MONSTERS HERE THAT I NEED TO PROTECT.

Sans:

It’s a beautiful day now outside 
Birds are singing, flowers blooming bright
Days like these should be full of light
But kids like you should be burning in [bad word] 
Human, are you ready for
fight between just you and me, together
Will I get to my revenge?
Or will you get to the end?

In your smile and in your eyes 
Are showing the real monster that’s within
 Killing them all one by one
 You feed it LOVE as you win 

Hey, tell me, do you wanna have a really bad time?
Do you think I am really gonna stand there and let go of all of your crimes?
Feel all of the sins crawl up your back 

Hey, tell me, can you look at all the things that you’ve done
Resetting everything over again, consuming skeleTONS of time
That determination needs to die 

Was it worth the cost?
All the lives that were lost
I warned you, can’t you see?
You chose to let them bleed

Even if she sees 
That promise, I can’t keep
Want to stay as friends?
Then [bad word] back again

Full [bad word] are you now?
I guess my job is going well somehow
If you try to go back the start
There will be no change inside my heart

The fight has only just begun
The time [bad word]  there’s nowhere [bad word] Now feel the endless agony
Cause this is the reality