Thanks a lot!
Yes, I use GameMaker.
The keyboard remapping system is controlled with an object that contains an array with all the default inputs and the current inputs, this data is constantly being fed by a save file with contains this information using GameMakers ini files. Then I update these files on the KeyChange_Screen when player wants to. Check out this video of how to manage save files in GM!
The light system is with surfaces. When game starts it creates a black surface that overlays with some alpha the application surface and everytime a player enters a room the surface is resized to this rooms dimensions so the camera doesn't affect it. To make the effect of light in the dark I apply a shader that I made to the surface. Here's how it works: for certain objects the light system creates a white circle centered on them on the black surface, and with the shader I make that just the black part shows off.And finally, programming jumping through platforms was somewhat tricky for me, I first made this platforms as a solid that just checks collision if player is above them, but then I also had to make a function that checks of this relative to the nearest platform using nearest_instance() because it was checking this with any platform not just with the below the player one.
I hope I gave you a decent answer to your questions.
Thanks again for checking out my game! :D