Strings, a very talented singer, is struggling with an incurable case of deep depression from heartbreak. When Twilight and Princess Cadance try to help him resolve his issues, they accidently turn him into an evil creature that intends to wipe out all Love in Equestria.

Lessons:

(Regardless if someone is being self-destructive)

-Commanding/Demanding/Bullying someone to "Let Go" and "Move on" only makes things worse, not better.
-You cannot force someone to change. It's their choice to make and theirs alone.
-People cannot simply change how the feel or who they want to love simply because you want them to.
-You can only *TRY* to help someone with their issues, but in the end, your efforts may not work.