Qualifiers were a charm to work with, but they did form a huge weight on my game. My guess is that for each of a qualifier's event, it calculates the actions for every single object in the qualifier rather than just the one it applies to (correct me if I'm wrong though).
Anyway, I did add these out of sight, out of mind events. However, the biggest problem lies in the objects that sooner or later will come in from the right. Though I made these objects "inactive when too far from window", my game becomes very slow when I make a longer than short level, even with all the physics objects still far away. It goes better when they are actually destroyed.
Hence the Mario comparison. With such little memory, they managed to make their levels so long. Is it perhaps impossible for objects with physics movements to be inactive? Is it because it constantly needs to calculate that all of their movements "stop" while they collide with the background, no matter how far away from the window?
Because if that's the case, I could make a complete static clone for each of them and create their physics version when you close in on them. But that just seems like such a strange workaround.. I once tried to give them a static movement and switch to "physics - static" when you get close, but that made them glitch terribly. I'm sure there should be a very simple solution out there I'm not seeing.