How do I make an animated background in AGS?
I believe (I've never done this):
1. Open the room you want to animate.
2. Click on the "Animating Backgrounds..." button.
3. Click the "New frame" button.
4. Choose the frame to import.
5. Import more frames by repeating steps 3 - 4.
Search the manual for more assistance.
But BTW, it's better (quicker load time/smaller file size) to just animate objects/characters if possible. Unless, like, more that 50% of the room should move at once... But, it's still your choice; it's there for a reason...
You'll need to import a background for the room first, and then the animation frames. The original background will be the first frame of the animation.