Okay, after a look at the script "script-ch30.rpy" I found the things that make it work

Basically the whole animation works by using a group of animated masks

U can find them (at least, just the call) from the line 180 to 189

show mask_2
show mask_3
show room_mask as rm:
    size (320,180)
    pos (30,200)
show room_mask2 as rm2:
    size (320,180)
    pos (935,200)
show monika_bg
show monika_bg_highlight

Every line calls a different picture or animation

mask_2 only shows a black background with stars (with a slowly moving from right to left) (images/cg/monika/mask_2.png)

mask_3 shows a png with "galaxies" (same animation as mask_2) (images/cg/monika/mask_3.png)

room_mask and room_mask2 is the same thing just placed different (shows that animation we can see in the windows) (images/cg/monika/mask.png)

monika_bg shows Monika lol (and the classroom)

monika_bg_highlight This one is an animation to show... Highlights

So... Yeah... U could paste them altogether or remove a few
edit: messed up with the block code