Thanks for your comment!
Yeah, I have the plugin open sourced as well but it does take a bit of messing around to get it working. My plan is to tidy up the plugin (and also make it a real plugin since right now it just overwrites the point and click scene) to make it more user friendly. I tried to do that as I went but I ended up hacking things up trying to get the game finished.
The smoothness comes from building the background/view from all the pieces off-screen and then doing a big copy from that "buffer" into the VRAM's on-screen space. An even better way would be to draw off-screen and then move the whole background like a swap for an instant update, but I didn't manage to get that working in the GB Studio context during the jam.