Thanks again for the help! I have one last question: is it possible to make an animated object somehow? I bought "Spaceguy Red Space" and I encoutnered a couple of animated talking characters so it should be possible, I just don't know how.
Viewing post in The Definitive Guide to the Raycasting Game Maker comments
Unfortunately no. The developer of RGM never implemented idle animations on sprite objects.
You can have 4-frame animated wall textures. And you can make enemies stationary so that you can create projectile turrets or things like that. The problem is that stationary enemies use a 0 in the speed parameter, so that means they aren't moving, and so they won't actually play their walking animation while at rest.
Sprites can be destructable, so they will play 5 frames of a death or destruction animation. But unlike the wall textures, sprites don't have an option for a 4-frame idle animation.
I just discovered how he did it: the maker somehow managed to turn non-moving "enemies" in animated NPC characters. Unfortunately he is no longer active in game development. The only issue I now have is white borders at the edges of my sprites but that's a matter of trial and error I guess, thanks again.