Game Maker 6.1 comes with an easy way to show an explosion when an instance is destroyed, actually, two new ways. One is a new action called Create an effect. The second way is the corresponding functions, effect_create_above() and effect_create_below() .
This tutorial will deal with the action. If you program with GML and want to use one of the functions, you can easily adapt the information in this tutorial for use with them, or, see their individual pages for more information on how they work.
This tutorial is for Game Maker 6.1 registered.
In the Destroy event of the object you want to explode, drag the Create an effect action into the action list. You can find it in the draw tab, at the bottom, in the section labeled other. It looks like an explosion. The Create an effect action window will pop up.
In the type box, choose "explosion". It is set to explosion by default, so you shouldn't have to change anything.
The values you put in the x and y box will depend on where the origin of the sprite of your object is.
By default, it is in the top-left corner, so if you haven't changed it, and you can put this in the x and y boxes :
x : x + sprite_width / 2 y : y + sprite_height / 2
If you have centered the origin of the sprite, simply put x and y in the x and y boxes, respectively.
Leave the size box as it is for now. After you have seen the actual size in relation to your object after is has been destroyed, you can change it to suit the size of your object.
In the color box, choose a red color.
In the where box, choose above objects.
Now, save your game and test it out. You know everything you need to know to make an object explode.