I tried messing with the code to see if it would be faster to use surface_copy in the mouse event. It might have helped a bit.. but I think the function ignores tranparency.

Othervise a nice and simple example but I suspect there's better ways to do it like maybe drawing everything to a surface and thereby avoiding creating and deleting sprites. That would of course still leave some transparency issues so I'm not gonna vote :)

A) You have to use sprites if you want fast pixel-perfect collisions
B) Sprites handily solve the transparency issues
C) Instead of deleting the sprite in the mouse event I could change it so that it deletes it the step after... That might work to speed it up but only marginally.

I haven't been experimenting with destructable terrain and I guess you're right for most parts.
I really think C) would be a worthwhile improvement because I noticed a big delay from when I clicked to when the hole appeared. Maybe it would be enough to simply redraw the screen before deleting the sprite. And A) well... it could be done in another step/moment as well.
But nice example as I wrote

lol, too slow

Good idea, but slow. I got 5-25FPS

kinda good, i still like your more complex version better though! 8/10

cool. I guess...I thought it was, so 9/10.