get the pixels of part of a costume?

I'm making a project and I was wondering, is there a way to make a sprite get the pixels of another sprite that it's touching, like make the sprite forever go to mouse and then it switches costumes to the pixels that it's touching so it looks like it's transparent, but it's not.

Will PASTE ON do what you want? (Have the other sprite do it to your sprite.)

thanks I never really tried paste on