Sprites, backgrounds, and tiles

You can use sprites, background images, and tiles the way you are used to in GameMaker (including
the use of color blending and alpha values). You cannot change background resources during game
play. You can though load sprite resources during game play. You can e.g. use this to show a series of
images without the need to put them all in the game (which would be using too much video
memory). Be careful though that all sprites you load will be stored in video memory. So you should
immediately delete a sprite you loaded when you don’t need it anymore. So to show a series of
images you would typically in code add a sprite resource from a file, display it, delete it, add a new
one, etc.
You should realize that sprites are far more optimized in the iOS and Android runner than the use of
backgrounds. Hence you are recommended to use backgrounds only as actual backgrounds in rooms
and for all other purposes use sprites. Although you can use tiles.
You can use particle systems and are recommended to use this  rather than using many different
instances whenever possible. Particle systems are much, much quicker than using many instances,
even if those instances only have a create event. They are also much simpler to optimize if you need
even more performance out of them down the line.
Make sure that for all images, sprites and backgrounds you have the rights to use them in a
commercial game. It works best is your team creates all of these itself. If not, better make sure you
have printed, signed statements that you have the right to use them. It is normally better to pay for
them than to get them for free. In that way it is clearer that you indeed have the rights. We demand
excellent quality graphics. Your game must stand out among the competitions. Otherwise it will be
difficult to sell it