With this function you can set the draw depth for the particle system, much the same as you can set the render depth of different layers within the room, where a low draw depth means that it will appear on top of all things drawn with a higher depth, and a high draw depth placing it below everything with a lower draw depth.
part_system_depth( ind, depth );
|ind||The index of the particle system to change.|
|depth||The depth at which to set the particle system.|
global.Sname = part_system_create();
part_system_depth(global.Sname, -1000 );
The above code will create a particle system and store its index in the global variable "Sname". this system is then given a low depth of -1000, meaning that it will appear above everything with a higher draw depth.