I've written a tutorial on how to make a superweapon that has a random effect - eg, it will randomly choose one of several attacks to use on an area. I've written it up as a third level satellite hack for the Infantry general's Internet center, allowing the hackers to hack into the targeting systems of off-map weapons and target them wherever you select.
It covers everything from modifying the internet center to use it, to the superweapon itself and everything associated with it - sounds, radial cursors, and the attacks themselves.
It's a bit(!) long to post here, you can read it
Here.