I did this as a collab with my awesome bro YAMGARDEN FROM DA!!!! She's amazing!!! She drew the sketch and I painted it XD COME CHECK HER OUT! yamsgarden.deviantart.com/ YAMsgarden 
CHECK OUT HER COMIC TO THIS PICTURE IT'S AWESOME!!!! COLLAB Farewell Undyne by YAMsgarden

ALSO COME SEE THIS HERE ON YOUTUBE!!! :D (Big Grin)

 www.youtube.com/watch?v=kCJAyl…

ALSO YES I CHANGED MY NAME!!! I'M WALKING MELONS! XD

WE JOINED FORCES and this is One of the results XD 
I know I did all the color work but I really have to hand it to YamGarden here, I NEVER would have come up with such a composition as brilliant as this. I mean you can even rule of thirds test it, it's freaking spot on the dollar! It's amazing and makes an incredible piece, so props and a round of applause to YamGarden!!! XD 

PLUS I DON'T KNOW WHAT HAPPENED BUT I THINK THIS IS MY BEST PAINTING JOB YET!!! SO YEAH 

This is YamGardens's idea. In Genocide Mode Undyne dies of course and melts before she turns into dust, and with Alphys having cameras everywhere, she probably watched the fight, and thus, Undyne dying. :C Which is SO SAD!!! And thus, this is where this picture comes in! She'll be posting a comic that leads up to this soon!, but it's not posted yet, but I'll make a link when it is!!!