Thanks jlnr, but that's EXACTLY what I wanna avoid. It's not even necessary to do it, you know. If I included a bug in the source code I was modifying, while I was trying to do something else, now sprites look as dwarves or sprites in the mythological sense. XD This means it can be done by default with a few additions. I know, I've already used a variable to let it change but that's only a disguised bug, so to say. Nope, it wasn't a Gosu::Image.scale_x or scale_y call, I've already discarded it. The window remained as big as originally intended.
Don't you recall where in the gosu code there was a place that was multiplied by some value that enlarged sprites displayed on screen?
I do remember we once discussed something on the discord channel about images being slightly enlarged by default in gosu, you'd said back then they'd look kind of tiny otherwise. Where's that part of the code? That part contains the key to implementing a "fake" scaling effect without needing the Gosu.scale(params) method call.