YES! That worked. Much appreciated.
For reference, if others struggle with the same:
I first set the variable Smashing to 2 when the block is created. Then when the ball hits the block, I subtract 1 from the variable Smashing.
Next, I create one event where I Compare the variable, and check if it's set to 1. If it is, I change the animation frame to 1 (to get the cracked block).
Finally, I check again in a new event, and see if the variable is 0. If it is, destroy the block.
This way, I can use multiple blocks pr level, as they all use individual variables. Adding more frames (to make the blocks harder) is a bit tricky, as you'll need to check for every single number of the variable, and take actions accordingly.
Also, I set all of this on a General Stuff-event sheet, then include it on every Level-specific event sheets. This way I only need to create the events for each block once, and I can do fun stuff with each individual level if I want to (like scripting sequences etc.)