I was trying to create a sprite flicker that started slow then got faster using a simple algorithm.
I failed.
In my giving up, I settled for this: a flicker kinda like a modern alarm clock (bee-bee-bee-beep...bee-bee-bee-beep...bee-bee-bee-beep). I'm not proud of it, but it was cool enough.
Couldn't you just do that by having a timer variable control image_alpha?
Like,
if timer>0{timer-=1}else{timer=0}
if timer=90{image_alpha=0}
if timer=86{image_alpha=1}
if timer=65{image_alpha=0}
if timer=60{image_alpha=1}
if timer=45{image_alpha=0}
if timer=40{image_alpha=1}
if timer=30{image_alpha=0}
if timer=25{image_alpha=1}
if timer=20{image_alpha=0}
if timer=17{image_alpha=1}
if timer=8{image_alpha=0}
if timer=6{image_alpha=1}
if timer=4{image_alpha=0}
if timer=3{image_alpha=1}
if timer=2{image_alpha=0}
if timer=1{image_alpha=1}
if timer=0{image_alpha=1}
I mean, I know you're way better and more advanced in GML than I am, but it seems to me that you're making this more complicated than it ought to be. I could be wrong, though, since you work with it a very specific way for this project of yours.