This has been thought of before, but no one has done it. So I present one of 3 options:

1: A sonic guitar that damages actors and crumbles walls with sharp musical notes.

2: An awesome riff guitar that heals friendly actors in a certain pixel range with awesomeness.

3: A combo of the above.

Someone please make this. Or if you supply a musical note sprite (or maybe 2 - the 2 legged and one legged note) and a guitar sprite, I can make option 1.

Been done loooooooong time ago.
Rest is meh.

When was it done and where?

During builds 11-13, most likely wiped from the face of the earth by now.
It's not that hard to make, you can do it yourself.

Indeed. If I am to do so though, I'm gonna need a spriter to do it. So can someone just dump a sprite here or something?

Knock yourself out.